Posts Tagged ‘rsyslog’

How to Install and Use Grafana Loki on Linux for mupltiple server Log Metrics Monitoring

Tuesday, March 31st, 2026

how-to-install-and-use-grafana-loki-on-linux-for-log-metrics-monitoring-for-multiple-server-observability-logo
Grafana Loki has become a popular choice for log management on Linux systems, nowadays, because free software like under AGPLv3 licence, it’s lightweight, cost-efficient, and integrates seamlessly with modern observability stacks. Unlike traditional log systems, Loki focuses on indexing metadata (labels) instead of full log content, which makes it especially attractive for Linux environments where logs can grow quickly.

Grafana Loki can be used to create fully featured logging stack. It has a small index and highly compressed chunks which simplifies the operation and significantly lowers the Storage expense of it.
Unlike other logging systems, Loki is built around the idea of only indexing metadata about your logs labels (just like Prometheus labels).
Log data itself is then compressed and stored in chunks in object stores such as Amazon Simple Storage Service (S3) or Google Cloud Storage (GCS), or even locally on the filesystem.

In this article will give you some real-world, practical usage of Loki on Linux, from its setup from zero to day-to-day use workflows.

Reasons why to use Loki on Linux ?

Linux systems generate logs mainly in /var/log but often used extra installed Apps tend to log in different locations for easier log distinguishment, e.g.
logs location might lack a good structure (be everywhere) :

Some common example locations, where logs are stored

  • /var/log/syslog
  • /var/log/auth.log
  • Application logs (/opt/app/logs/*.log)
  • Container logs, are kept within respective container ( Docker /  PodMan Kubernetes )

Sonner or later if you have to manage a large infrastructure of servers you end up, it is pretty easy to end up in a log mess.

This is exaclty where Loki helps you solve:

  • Centralize logs from multiple machines (within Grafana)
  • Search logs efficiently using log craeted labels
  • Correlate logs with metrics in Grafana

Loki Architecture Overview


loki-use-stack-chain-diagram-from-cloud-to-grafana

A typical Loki setup on Linux has 3 components:

  1. Loki server -> stores and queries logs
  2. Promtail -> collects logs from the around the system
  3. Grafana -> Use it to visualizes and queries logs

Promtail acts like a lightweight agent that tails log files and sends them to Loki.

I. Installing Loki on Linux

1. Download Loki

$ cd /usr/local/src
$ wget https://github.com/grafana/loki/releases/latest/download/loki-linux-amd64
$ chmod +x loki-linux-amd64
# mv loki-linux-amd64 /usr/local/bin/loki

2. Create a simple config like

auth_enabled: false

server:
  http_listen_port: 3100

ingester:
  lifecycler:
    address: 127.0.0.1
  chunk_idle_period: 5m

schema_config:
  configs:
    – from: 2020-10-24
      store: boltdb-shipper
      object_store: filesystem
      schema: v11
      index:
        prefix: index_
        period: 24h

storage_config:
  filesystem:
    directory: /var/lib/loki/chunks

3. Run Loki

# loki -config.file=loki.yaml


Hopefully if all is okay with loki.yaml config the service will start.

a. Installing Promtail (Log Collection)

Example  config (to modify to your preferences):

scrape_configs:
  – job_name: linux-logs
    static_configs:
      – targets:
          – localhost
        labels:
          job: syslog
          host: my-linux-server
          __path__: /var/log/*.log

This collects all logs in /var/log/ and labels them.

b. Run Promtail

# promtail -config.file=promtail.yaml

! Note that loki and promtail it is run as root (to have permissions to files which will be processed). This is not the best practice, so for security reasons,
if you have the necessery storage move out the files to a central log aggregator directory with a script set a unprevileged non-root user for it and run the services with those user.

c. Run loki / promtail as non-root user:

Once tested it runs, it is good idea to run two tools with non-root user, i.e.:
Run promtail as a dedicated user (e.g., promtail).

Add that user to groups like:

adm (for /var/log)

systemd-journal (for journal logs)
Adjust file permissions if needed

# useradd –system –no-create-home promtail
# usermod -aG adm promtail

$ loki -config.file=loki.yaml
$ promtail -config.file=promtail.yaml

II. Practical Use Cases of Loki on Linux

1. System Troubleshooting

One good use of Loki is to Search for errors in syslog:

{job="syslog"} |= "error"

By this you can Quickly diagnose:

  • Boot issues
  • Service failures
  • Kernel errors

2. SSH Login Monitoring

Track login attempts from /var/log/auth.log for many VM hosts:

{job="syslog"} |= "sshd"

You can detect:

  • Failed login attempts
  • Brute-force attacks
  • Unauthorized access

3. Application Debugging (look for exceptions)

If your app logs to /var/log/app.log and you App running it, to get a view on java thrown exceptions:

{job="app"} |= "exception"

This use case can Help developers to:

  • Trace bugs
  • Monitor runtime issues
  • Correlate logs with deployments

4. Multi-Server Log Aggregation

Once you run Promtail on multiple Linux servers:

labels:
  host: server1

Then you can do query to extract collected data for each one if it:

{job="syslog", host=~"server1|server2"}

This makes multiple machines behave like one unified log source.

5. Log-Based Metrics

You can extract metrics from logs:

count_over_time({job="syslog"} |= "error" [5m])

Use this for:

  • Alerting
  • Error rate tracking
  • Incident detection

III. Using Grafana for Visualization

In Grafana, you can:

  • View logs in real time
  • Build dashboards
  • Create alerts based on log patterns

Example use would be:

Create Grafana Panel showing error rate per host and Alert when errors exceed a threshold.

loki-log-drill-down-sample-in-grafana

Good Practices on Loki use

1. Always Use Meaningful Labels

Example for Good label should contain as many descriptory parameters as possible:

labels:
  app: nginx
  env: prod
  virtualization: vmware
  type: Middleware
  service:: proxy
  Customer: customerA

Bad obscure label:

labels:
  request_id: 123456  


2. Avoid Too many Unique labels

Keep in mind Too many unique labels leads to poor performance !.

3. Rotate Logs Properly and optimize with Secure Loki Endpoint

Loki won't manage your internal logs, as it can well complement ( but not replaces ), on Server / VM traditional tools like journalctl / grep / logrotate. but just give you a better overview of what is inside of service spit logs based on easy to give criterias from Grafana.
You will still need usually at best scenario to  setup of a Central Logging Server (to store all Infrastucture logs).
Consider also that sending data from your logs with Loki, like with a zabbix client it is always a idea to have reverse proxy like NGINX or Haproxy to reduce Network bandwith and for better management centralization of the infra.

4. Secure Loki Endpoint

  • Use reverse proxy (NGINX)
  • Enable authentication in production

Closure Summary

On Linux, Grafana Loki can help when:

  • You have multiple servers
  • Logs are growing fast
  • You need centralized  and relatively easy observability

Loki has its downtimes too as processing the logs to really extract data hits a high CPU use. Running it on a multiple machines is useful,
especially if your machines has high unutilized CPU IDLE time and you want to make the log data collection per server based being so to say partially duplicated and indepdendent from centralized logging. .
For high scale infrastructure, however sysadmins prefer to use an ELK OpenSearch Stack or log databases such as:
VictoriaLogs. With having infrastrcture of 100 servers or so perhaps setting up with some Ansible automation Loki makes sense.
Loki is not meant to replace databases or full-text search engines, but great often for simple  log aggregation and analysis and of the simplistic tools available today.

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Posted in Cloud services, Linux, Monitoring, System Administration | No Comments »

Linux Bash Logging log everything. Prevent user from delete his history and keep record of every command User ever Run

Tuesday, March 17th, 2026

make_bash_history_permanent-how-to-keep-every-user-command-forever-prevent-users-from-deleting-their-bash-history-on-linux

Whether you're managing servers, writing scripts, or troubleshooting complex systems, one of the most valuable tools at your disposal is your command history. But the default Bash history has serious limitations: it’s easy to lose, doesn't timestamp by default, and doesn't log everything in real time.

What if you could keep a permanent, timestamped, real-time log of every command you ever run in Bash?

Good news: you can.

In this guide, we’ll walk through how to set up robust, automatic Bash logging to track every command you type—across sessions, with full timestamps, and even with user and host information. Ideal for system administrators, developers, auditors, or anyone who wants to maintain a clear, searchable audit trail.

Why Bash Logging Persistence So Important ?

Before we dive into the how, let's understand the why:

  • Accountability – Know exactly what commands were run, by whom, and when.
  • Auditability – Great for security reviews or compliance requirements.
  • Troubleshooting – Trace back actions that caused issues.
  • Documentation – Reuse commands or share with teammates.
  • Forensics – Investigate suspicious activity.

How Bash History Behaves  ( By Default )

Without any config everyone knows , Bash uses a file called ~/.bash_history in $HOME to save command history.

What is tricky here:

  • .bash_history not written to immediately – only when the session exits.
  • It can be overwritten by other sessions.
  • It lacks timestamps unless explicitly configured.
  • It doesn’t log failed attempts or commands from other users.

In this short article I'll show you one of the ways on how to make .bash_history keeps the record for you even though some user tries to hide tihngs by running the commands and exiting the shell abnormally by killing it with the well known command by hackers and sysadmin gurus:


$ kill -9 $$

The command forces the user you have logged into to kill the process of the bash (-bash). 

Here is how.

Enable Advanced Bash Logging

1. Enable Timestamps in History

Add this line to your ~/.bashrc or ~/.bash_profile:

export HISTTIMEFORMAT="%F %T "

This formats the date/time as YYYY-MM-DD HH:MM:SS.

After modifying the file, run:

source ~/.bashrc

Now, run:

history

And you’ll see timestamps next to your commands.

2. Increase History Size

The default history size is often too small. Let’s increase it:

export HISTSIZE=100000

export HISTFILESIZE=200000


Add these to ~/.bashrc as well.

3. Log Commands Immediately (Across Sessions)

By default, Bash only writes history when the shell exits. To log commands in real time, add the following to ~/.bashrc:

# Append to the history file, don't overwrite it

shopt -s histappend

# Immediately append command to history file after execution

PROMPT_COMMAND='history -a; history -n'

Explanation:

  • history -a: Append current session's command to ~/.bash_history
  • history -n: Read any new lines from the file (from other sessions)

4. Log All Commands to a Separate File (for each User)

To keep a separate, detailed log, you can use the trap command in combination with logger, or write to a custom file.

Add this to your ~/.bashrc:

LOG_FILE="$HOME/.bash_command_log"

trap 'echo "$(date "+%F %T") | $(whoami)@$(hostname) | $(pwd) | $BASH_COMMAND" >> "$LOG_FILE"' DEBUG

This logs every command as for example:

2025-10-10 14:25:02 | master_app@server01 | /var/www | systemctl restart nginx

This file can grow large over time – consider rotating it regularly with logrotate or similar tools.
To prevent the file 100% from being modified by the user itself you can make the log file  immutable with command

# chattr +i $HOME/.bash_command_log


5. Guarantee log security, Make copy of Logs to prevent hackers to modify them

If logging for audit/security purposes:

  • Store logs in append-only files (chattr +a logfile on ext4 FS)
  • store files with rsyslog service (see below)
  • Use remote logging (e.g., send via logger to syslog  / rsyslog or any other centralized logging service) / logcollector etc.
  • Monitor for tampering or suspicious gaps

6. Store file with rsyslog service

Create the file and set it proper permissions

# touch /var/log/bash_audit.log
# chmod 600 /var/log/bash_audit.log
# chown root:root /var/log/bash_audit.log

# vim /etc/rsyslog.d/bash_audit.conf

Add:

if $programname == 'bash_audit' then /var/log/bash_audit.log
& stop

# systemctl restart rsyslog


To later verify it works fine

# tail -f /var/log/bash_audit.log
# journalctl -t bash_audit

 

6. Add Global Bash Logging for All Users

Assuming that the bash_audit set program / name tag is already done as in step 5.
To apply logging system-wide, Edit /etc/profile /etc/bash_profile or /etc/bash.bashrc and include the same trap cmd and logging is ready. Ensure:

  • The log file is writable by users (or add users to a group that can append to file) or modify the command to use sudo logger for centralized syslog.
  • You test it carefully before deploying to all users.

     

     

     

    An improved wide user version of trap command would be something like this

# Bash command logging (readable layer)

trap 'CMD=$(history 1 | sed "s/^[ ]*[0-9]\+[ ]*//");
MSG="$(date "+%F %T") | $(whoami)@$(hostname) | $(pwd) | $CMD";

/usr/bin/logger -t bash_audit "$MSG"
' DEBUG

Make these two env variables read only for additional hardening 

readonly PROMPT_COMMAND
readonly HISTFILE

Note that you will need to edit passwordless login for sudo to logger

  • Setup auditd to make file read only

# apt install auditd audispd-plugins –yes

  • Test it with auditctl

# auditctl -a always,exit -F arch=b64 -S execve -F auid>=1000 -F auid!=4294967295 -k cmdlog
# auditctl -a always,exit -F arch=b32 -S execve -F auid>=1000 -F auid!=4294967295 -k cmdlog

  • Make rules permanent via cmdlog.rules

# vim /etc/audit/rules.d/cmdlog.rules

-a always,exit -F arch=b64 -S execve -F auid>=1000 -F auid!=4294967295 -k cmdlog
-a always,exit -F arch=b32 -S execve -F auid>=1000 -F auid!=4294967295 -k cmdlog

  • Load and lock audit rules

# augenrules –load
# auditctl -e 2

  • Check audit logs

# ausearch -k cmdlog -i
exe="/usr/bin/ls" argc=1 a0="ls"

7. Rotate Log Files Automatically with logrotate

Create a logrotate config like /etc/logrotate.d/bash_command_log:

/home/*/.bash_command_log {
daily
rotate 7
compress
missingok
notifempty
}

/var/log/bash_audit.log {
daily
rotate 7
compress
missingok
notifempty
}


This keeps logs for 7 days and compresses old ones.

8. Test Every command Logging is permanenty stored

After setting bash logging up up:

  1. Open a new terminal client with SSH session
  2. Run a few commands
  3. Check ~/.bash_command_log (or your alternative configured log location)

You should see a real-time record of every command executed.

Use tools like grep, awk, or fzf Command fuzzy finder to search through your command log efficiently. Example:

grep apt ~/.bash_command_log

You can further automate it and deploy it to multiple servers with Ansible or some shell scripting.
If you need it Ask me how to automate it?
Ask me how to automate it with Ansible or a shell script.

Wrapping it Up

With just a few lines in Bash config, basic history feature becomes a persistent, and timestamped static record  that’s invaluable for system admins, developers, and security teams.

Summary Checklist

  • Enable HISTTIMEFORMAT
  • Increase history size
  • Append history in real time
  • Log every command with trap DEBUG
  • Optionally send to rsyslog / syslogd / systemd-journald or other central log server (Fluentd / ELK Stack / Graylog)
  • Rotate logs with logrotate

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Posted in Curious Facts, Linux, Security, System Administration | No Comments »

How to log multiple haproxy server instance processes on single server in seperate files with rsyslog filters

Monday, February 3rd, 2025

haproxy-log-frontend-backend-and-transferred-connections-in-separate-log-files-on-linux-server-logo

Lets say you want to have 2 separates instances of haproxy and log the output to separate files, how this can be achived?

In this article, i'll tell in few easy steps how to enable multiple haproxy server instances created on the same Linux server / VPS or docker container to run and log its served content in separate log files without using separate file logging handlers "local"s.
The task might be helpful for people who are involved with DevOps and has to route separate proxy traffic on same linux machine.
 

Lets say you have the following haproxy process instances running with separate haproxy configs:
 

1. haproxy
2. haproxy_worker2
3. haproxy_worker3
 

List of processes on the Linux host would looks like that.

[root@linux-server rsyslog.d]# ps -ef|grep -i hap
root     1151275 1147138  0 11:58 pts/2    00:00:00 grep –color=auto -i hap
root     1835200       1  0 Jan30 ?        00:00:00 /usr/sbin/haproxy -Ws -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid
haproxy  1835203 1835200  0 Jan30 ?        00:10:41 /usr/sbin/haproxy -Ws -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid
root     1835216       1  0 Jan30 ?        00:00:00 /usr/sbin/haproxy_worker2 -Ws -f /etc/haproxy/haproxy_worker2.cfg -p /run/haproxy_worker2.pid
haproxy  1835219 1835216  0 Jan30 ?        00:02:46 /usr/sbin/haproxy_worker2 -Ws -f /etc/haproxy/haproxy_worker2.cfg -p /run/haproxy_worker2.pid
root     1835216       1  0 Jan30 ?        00:00:00 /usr/sbin/haproxy_worker3 -Ws -f /etc/haproxy/haproxy_worker3.cfg -p /run/haproxy_worker3.pid
haproxy  1835219 1835216  0 Jan30 ?        00:02:46 /usr/sbin/haproxy_worker3 -Ws -f /etc/haproxy/haproxy_worker3.cfg -p /run/haproxy_worker3.pid

Question is how to log the 3 haproxies passed through configured connection IP and frontend / backend outputs to separate files

 /var/log/haproxy.log , /var/log/haproxy_worker2.log and /var/log/haproxy_worker3.log


To achieve the task, you will need to set-up 3 rsyslog config files name it according to your preferences and make sure no other rsyslog
file with haproxy related configuration does not mess up with the configs (e.g. is not having a config start number NUMBER_file.conf prior to the below created files.

Then create lets say 49_haproxy.conf and 50_haproxy_worker2.conf and 51_haproxy_worker3.conf

[root@linux-server rsyslog.d]# cat 48_haproxy.conf
#$ModLoad imudp
$UDPServerAddress 127.0.0.1
$UDPServerRun 514
#2022/02/02: HAProxy logs to local6, save the messages
# Template to include only the timestamp in HAProxy logs
template(name="HaproxyTimestampOnly" type="string" string="%timegenerated% %msg:::drop-last-lf%\n")
local6.*                /var/log/haproxy.log;HaproxyTimestampOnly
# Apply the template to HAProxy prod port mapping logs
#if $programname startswith 'haproxy[' then /var/log/haproxy.log;HaproxyTimestampOnly
& stop

[root@linux-server rsyslog.d]# cat 50_haproxy_worker2.conf
$ModLoad imudp
$UDPServerAddress 127.0.0.1
$UDPServerRun 514
# Template to include only the timestamp in HAProxy logs
template(name="HaproxyTimestampOnly" type="string" string="%timegenerated% %msg:::drop-last-lf%\n")

# Apply the template to HAProxy prod port mapping logs
if $programname startswith 'haproxy_worker2' then /var/log/haproxy_worker2.log;HaproxyTimestampOnly

 

[root@linux-server rsyslog.d]# cat 51_haproxy_worker3.conf
$ModLoad imudp
$UDPServerAddress 127.0.0.1
$UDPServerRun 514
# Template to include only the timestamp in HAProxy logs
template(name="HaproxyTimestampOnly" type="string" string="%timegenerated% %msg:::drop-last-lf%\n")

# Apply the template to HAProxy prod port mapping logs
if $programname startswith 'haproxy_worker3' then /var/log/haproxy_worker3.log;HaproxyTimestampOnly

Those rsyslog configs permissions has to be as follows:

[root@linux-server home]# ls -al /etc/rsyslog.d/48_haproxy.conf
-rw-r–r– 1 root root 488 Jan 30 12:44 /etc/rsyslog.d/48_haproxy.conf
[root@linux-server home]# ls -al /etc/rsyslog.d/50_haproxy_worker2.conf
-rw-r–r– 1 root root 379 Jan 30 12:45 /etc/rsyslog.d/50_haproxy_worker2.conf
[root@linux-server home]# ls -al /etc/rsyslog.d/51_haproxy_worker2.conf
-rw-r–r– 1 root root 379 Jan 30 12:45 /etc/rsyslog.d/51_haproxy_worker2.conf

 

The permissions for files to log the haproxy has to be as so:

[root@linux-server home]# ls -al /var/log/haproxy.log
-rw-r—– 1 haproxy haproxy 5014349 Feb  3 12:11 /var/log/haproxy.log
[root@linux-server home]# ls -al /var/log/haproxy_worker2.log
-rw-r—– 1 root root 728139 Feb  3 12:11 /var/log/haproxy_worker2.log
[root@linux-server home]# ls -al /var/log/haproxy_worker3.log
-rw-r—– 1 root root 728139 Feb  3 12:11 /var/log/haproxy_worker3.log

To make the changes take affect restart consequentially rsyslog first and then the 3 haproxy instances:

[root@linux-server home]# systemctl restart rsyslog
[root@linux-server home]# systemctl restart haproxy
[root@linux-server home]# systemctl restart haproxy2
[root@linux-server home]# systemctl restart haproxy3

Go on and check the logs that everything comes in from the haproxys running the same server into the separate files:

[root@linux-server home]# tail -f /var/log/haproxy.log /var/log/haproxy_worker2.log /var/log/haproxy_worker3.log
…

Hope this has helped someone out there looking to solve on how to log multiple haproxy instances on the same servers into separate files.

That's all folks. Enjoy!

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Posted in Everyday Life, Haproxy, Linux | No Comments »

How to log multiple haproxy / apache / mysql instance via haproxy log-tagging / Segregating log management for multiple HAProxy instances using rsyslog

Tuesday, May 23rd, 2023

rsyslog-logo-picture-use-programname-and-haproxy-log-tag-directives-together-to-log-as-many-process-streams-as-you-like

 

Introduction

This article provides a guide on refining haproxy  logging mechanism by leveraging the `programname` property in rsyslog, coupled with the `log-tag` directive in haproxy.
This approach will create a granular logging setup, separating logs according to their originating services and specific custom tags, enhancing overall log readability.

Though the article is written concretely for logging multiple log streams from haproxy this can be successfully applied
for any other Linux service to log as many concrete log-tagged data streams as you prefer.

Scope

The guide focuses on tailoring the logging mechanisms for two haproxy  instances named `haproxy` and `haproxyssl`, utilizing the `programname` property in rsyslog and the `log-tag` directive in haproxy for precise log management.

The haproxy and haproxyssl instances are two separate systemd config file prepared instances.
haproxy instance is simple haproxy proxying tcp traffic in non-encrypted form, whether haproxyssl is a special instance
prepared to tunnel the incoming http traffic in ssl form. Both instances of haproxy runs as a separate processes on the server.

Here is the systemd configuration of haproxy systemd service file:

# cat /usr/lib/systemd/system/haproxy.service
[Unit]
Description=HAProxy Load Balancer
After=network-online.target
Wants=network-online.target

[Service]
Environment="CONFIG=/etc/haproxy/haproxy.cfg" "PIDFILE=/run/haproxy.pid"
EnvironmentFile=/etc/sysconfig/haproxy
ExecStartPre=/usr/sbin/haproxy -f $CONFIG -c -q $OPTIONS
ExecStart=/usr/sbin/haproxy -Ws -f $CONFIG -p $PIDFILE $OPTIONS
ExecReload=/usr/sbin/haproxy -f $CONFIG -c -q $OPTIONS
ExecReload=/bin/kill -USR2 $MAINPID
SuccessExitStatus=143
KillMode=mixed
Type=notify

[Install]
WantedBy=multi-user.target


As well as the systemd service configuration for haproxyssl:
 

# cat /usr/lib/systemd/system/haproxyssl.service
[Unit]
Description=HAProxy Load Balancer
After=network-online.target
Wants=network-online.target

[Service]
Environment="CONFIG=/etc/haproxy/haproxy_ssl_prod.cfg" "PIDFILE=/run/haproxy_ssl_prod.pid"
EnvironmentFile=/etc/sysconfig/haproxy
ExecStartPre=/usr/sbin/haproxyssl -f $CONFIG -c -q $OPTIONS
ExecStart=/usr/sbin/haproxyssl -Ws -f $CONFIG -p $PIDFILE $OPTIONS
ExecReload=/usr/sbin/haproxyssl -f $CONFIG -c -q $OPTIONS
ExecReload=/bin/kill -USR2 $MAINPID
SuccessExitStatus=143
KillMode=mixed
Type=notify

[Install]
WantedBy=multi-user.target

 

Step 1: Configuring HAProxy instances with `log-tag`
 

To distinguish between logs from two HAProxy instances, `log-tag` directive is used to add tags to logs. This tag is used to filter these logs in rsyslog.
Modify the HAProxy configuration file in `/etc/haproxy/haproxy.*.cfg`

HAProxy Instance 1 (haproxy)
 

#———————————————————————
# Global settings
#———————————————————————
global
      log          127.0.0.1 local6 debug
      log-tag      haproxy

HAProxy Instance 2 (haproxyssl)


#———————————————————————
# Global settings
#———————————————————————
global
    log          127.0.0.1 local5 debug
    log-tag      haproxyssl

 

Step 2: Implementing rsyslog configuration for haproxy logs
 

Next, create a new rsyslog configuration file, stored in /etc/rsyslog.d/. Ensure the new configuration file ends in `.conf`

HAProxy Instance 1 (haproxy)

Now add rsyslog rules to filters logs based on the `programname` and the custom log tag:
 

# vi /etc/rsyslog.d/55_haproxy.conf
if $programname == 'haproxy' then /var/log/haproxy.log
&stop

HAProxy Instance 2 (haproxyssl)
# vi /etc/rsyslog.d/51_haproxy_ssl.conf
if $programname == 'haproxy_ssl' then /var/log/haproxy_ssl.log
&stop


These rules filter logs that originate from haproxy  and contain the respective string haproxy   or haproxy_ssl , directing them to their respective log files. The `& stop` directive ensures that rsyslog stops processing the log once a match is found, preventing dublication.

Finally, restart both the haproxy and rsyslog services for the changes to take effect:

# systemctl restart haproxy
# systemctl restart haproxyssl
# systemctl restart rsyslog


Reading References

haproxy:   log-tag directive

rsyslog:    rsyslogd documentation

This is a guest article originally written by: Dimitar Paskalev, guest blogging with good interesting articles is always mostly welcome 

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Posted in Educational, Hacks, Linux | 1 Comment »

How to configure multiple haproxies and frontends to log in separate log files via rsyslog

Monday, September 5th, 2022

log-multiple-haproxy-servers-to-separate-files-log-haproxy-froentend-to-separate-file-haproxy-rsyslog-Logging-diagram
In my last article How to create multiple haproxy instance separate processes for different configuration listeners,  I've shortly explained how to create a multiple instances of haproxies by cloning the systemd default haproxy.service and the haproxy.cfg to haproxyX.cfg.
But what if you need also to configure a separate logging for both haproxy.service and haproxy-customname.service instances how this can be achieved?

The simplest way is to use some system local handler staring from local0 to local6, As local 1,2,3 are usually used by system services a good local handler to start off would be at least 4.
Lets say we already have the 2 running haproxies, e.g.:

[root@haproxy2:/usr/lib/systemd/system ]# ps -ef|grep -i hapro|grep -v grep
root      128464       1  0 Aug11 ?        00:01:19 /usr/sbin/haproxy -Ws -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -S /run/haproxy-master.sock
haproxy   128466  128464  0 Aug11 ?        00:49:29 /usr/sbin/haproxy -Ws -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -S /run/haproxy-master.sock
root      346637       1  0 13:15 ?        00:00:00 /usr/sbin/haproxy-customname-wrapper -Ws -f /etc/haproxy/haproxy_customname_prod.cfg -p /run/haproxy_customname_prod.pid -S /run/haproxy-customname-master.sock
haproxy   346639  346637  0 13:15 ?        00:00:00 /usr/sbin/haproxy-customname-wrapper -Ws -f /etc/haproxy/haproxy_customname_prod.cfg -p /run/haproxy_customname_prod.pid -S /run/haproxy-customname-master.sock


1. Configure local messaging handlers to work via /dev/log inside both haproxy instance config files
 

To congigure the separte logging we need to have in /etc/haproxy/haproxy.cfg and in /etc/haproxy/haproxy_customname_prod.cfg the respective handlers.

To log in separate files you should already configured in /etc/haproxy/haproxy.cfg something like:

 

global
        stats socket /var/run/haproxy/haproxy.sock mode 0600 level admin #Creates Unix-Like socket to fetch stats
        log /dev/log    local0
        log /dev/log    local1 notice
#       nbproc 1
#       nbthread 2
#       cpu-map auto:1/1-2 0-1
        nbproc          1
        nbthread 2
        cpu-map         1 0
        cpu-map         2 1
        chroot /var/lib/haproxy
        user haproxy
        group haproxy
        daemon
        maxconn 99999

defaults
        log     global
        mode    tcp


        timeout connect 5000
        timeout connect 30s
        timeout server 10s

    timeout queue 5s
    timeout tunnel 2m
    timeout client-fin 1s
    timeout server-fin 1s

    option forwardfor
        maxconn 3000
    retries                 15

frontend http-in
        mode tcp

        option tcplog
        log global
 

        option logasap
        option forwardfor
        bind 0.0.0.0:80

default_backend webservers_http
backend webservers_http
    fullconn 20000
        balance source
stick match src
    stick-table type ip size 200k expire 30m

        server server-1 192.168.1.50:80 check send-proxy weight 255 backup
        server server-2 192.168.1.54:80 check send-proxy weight 254
        server server-3 192.168.0.219:80 check send-proxy weight 252 backup
        server server-4 192.168.0.210:80 check send-proxy weight 253 backup
        server server-5 192.168.0.5:80 maxconn 3000 check send-proxy weight 251 backup

For the second /etc/haproxy/haproxy_customname_prod.cfg the logging configuration should be similar to:
 

global
        stats socket /var/run/haproxy/haproxycustname.sock mode 0600 level admin #Creates Unix-Like socket to fetch stats
        log /dev/log    local5
        log /dev/log    local5 notice
#       nbproc 1
#       nbthread 2
#       cpu-map auto:1/1-2 0-1
        nbproc          1
        nbthread 2
        cpu-map         1 0
        cpu-map         2 1
        chroot /var/lib/haproxy
        user haproxy
        group haproxy
        daemon
        maxconn 99999

defaults
        log     global
        mode    tcp

 

2. Configure separate haproxy Frontend logging via local5 inside haproxy.cfg
 

As a minimum you need a configuration for frontend like:

 

frontend http-in
        mode tcp

        option tcplog
        log /dev/log    local5 debug
…..
….
…
..
.

Of course the mode tcp in my case is conditional you might be using mode http etc. 


3. Optionally but (preferrably) make local5 / local6 handlers to work via rsyslogs UDP imudp protocol

 

In this example /dev/log is straightly read by haproxy instead of sending the messages first to rsyslog, this is a good thing in case if you have doubts that rsyslog might stop working and respectively you might end up with no logging, however if you prefer to use instead rsyslog which most of people usually do you will have instead for /etc/haproxy/haproxy.cfg to use config:

global
    log          127.0.0.1 local6 debug

defaults
        log     global
        mode    tcp

And for /etc/haproxy_customname_prod.cfg config like:

global
    log          127.0.0.1 local5 debug

defaults
        log     global
        mode    tcp

If you're about to send the haproxy logs directly via rsyslog, it should have enabled in /etc/rsyslog.conf the imudp module if you're not going to use directly /dev/log

# provides UDP syslog reception
module(load="imudp")
input(type="imudp" port="514")

 

4. Prepare first and second log file and custom frontend output file and set right permissions
 

Assumably you already have /var/log/haproxy.log and this will be the initial haproxy log if you don't want to change it, normally it is installed on haproxy package install time on Linux and should have some permissions like following:

root@haproxy2:/etc/rsyslog.d# ls -al /var/log/haproxy.log
-rw-r–r– 1 haproxy haproxy 6681522  1 сеп 16:05 /var/log/haproxy.log


To create the second config with exact permissions like haproxy.log run:

root@haproxy2:/etc/rsyslog.d# touch /var/log/haproxy_customname.log
root@haproxy2:/etc/rsyslog.d# chown haproxy:haproxy /var/log/haproxy_customname.log

Create the haproxy_custom_frontend.log file that will only log output of exact frontend or match string from the logs
 

root@haproxy2:/etc/rsyslog.d# touch  /var/log/haproxy_custom_frontend.log
root@haproxy2:/etc/rsyslog.d# chown haproxy:haproxy  /var/log/haproxy_custom_frontend.log


5. Create the rsyslog config for haproxy.service to log via local6 to /var/log/haproxy.log
 

root@haproxy2:/etc/rsyslog.d# cat 49-haproxy.conf
# Create an additional socket in haproxy's chroot in order to allow logging via
# /dev/log to chroot'ed HAProxy processes
$AddUnixListenSocket /var/lib/haproxy/dev/log

# Send HAProxy messages to a dedicated logfile
:programname, startswith, "haproxy" {
  /var/log/haproxy.log
  stop
}

 

Above configs will make anything returned with string haproxy (e.g. proccess /usr/sbin/haproxy) to /dev/log to be written inside /var/log/haproxy.log and trigger a stop (by the way the the stop command works exactly as the tilda '~' discard one, except in some newer versions of haproxy the ~ is no now obsolete and you need to use stop instead (bear in mind that ~ even though obsolete proved to be working for me whether stop not ! but come on this is no strange this is linux mess), for example if you run latest debian Linux 11 as of September 2022 haproxy with package 2.2.9-2+deb11u3.
 

6. Create configuration for rsyslog to log from single Frontend outputting local2 to /var/log/haproxy_customname.log
 

root@haproxy2:/etc/rsyslog.d# cat 48-haproxy.conf
# Create an additional socket in haproxy's chroot in order to allow logging via
# /dev/log to chroot'ed HAProxy processes
$AddUnixListenSocket /var/lib/haproxy/dev/log

# Send HAProxy messages to a dedicated logfile
#:programname, startswith, "haproxy" {
#  /var/log/haproxy.log
#  stop
#}
# GGE/DPA 2022/08/02: HAProxy logs to local2, save the messages
local5.*                                                /var/log/haproxy_customname.log
 


You might also explicitly define the binary that will providing the logs inside the 48-haproxy.conf as we have a separate /usr/sbin/haproxy-customname-wrapper in that way you can log the output from the haproxy instance only based
on its binary command and you can omit writting to local5 to log via it something else 🙂

root@haproxy2:/etc/rsyslog.d# cat 48-haproxy.conf
# Create an additional socket in haproxy's chroot in order to allow logging via
# /dev/log to chroot'ed HAProxy processes
$AddUnixListenSocket /var/lib/haproxy/dev/log

# Send HAProxy messages to a dedicated logfile
#:programname, startswith, "haproxy" {
#  /var/log/haproxy.log
#  stop
#}
# GGE/DPA 2022/08/02: HAProxy logs to local2, save the messages

:programname, startswith, "haproxy-customname-wrapper " {
  /var/log/haproxy_customname.log
  stop
}

 

7. Create the log file to log the custom frontend of your preference e.g. /var/log/haproxy_custom_frontend.log under local5 /prepare rsyslog config for
 

root@haproxy2:/etc/rsyslog.d# cat 47-haproxy-custom-frontend.conf
$ModLoad imudp
$UDPServerAddress 127.0.0.1
$UDPServerRun 514
#2022/02/02: HAProxy logs to local6, save the messages
local4.*                                                /var/log/haproxy_custom_frontend.log
:msg, contains, "https-in" ~

The 'https-in' is my frontend inside /etc/haproxy/haproxy.cfg it returns the name of it every time in /var/log/haproxy.log therefore I will log the frontend to local5 and to prevent double logging inside /var/log/haproxy.log of connections incoming towards the same frontend inside /var/log/haproxy.log, I have the tilda symbol '~' which instructs rsyslog to discard any message coming to rsyslog with "https-in" string in, immediately after the same frontend as configured inside /etc/haproxy/haproxy.cfg will output the frontend operations inside local5.


!!! Note that for rsyslog it is very important to have the right order of configurations, the configuration order is being considered based on the file numbering. !!!
 

Hence notice that my filter file number 47_* preceeds the other 2 configured rsyslog configs.
 

root@haproxy2:/etc/rsyslog.d# ls -1
47-haproxy-custom-frontend.conf
48-haproxy.conf
49-haproxy.conf

This will make 47-haproxy-custom-frontend.conf to be read and processed first 48-haproxy.conf processed second and 49-haproxy.conf processed third.


8. Reload rsyslog and haproxy and test

 

root@haproxy2: ~# systemctl restart rsyslog
root@haproxy2: ~# systemctl restart haproxy
root@haproxy2: ~# systemctl status rsyslog

● rsyslog.service – System Logging Service
     Loaded: loaded (/lib/systemd/system/rsyslog.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2022-09-01 17:34:51 EEST; 1s ago
TriggeredBy: ● syslog.socket
       Docs: man:rsyslogd(8)
             man:rsyslog.conf(5)
             https://www.rsyslog.com/doc/
   Main PID: 372726 (rsyslogd)
      Tasks: 6 (limit: 4654)
     Memory: 980.0K
        CPU: 8ms
     CGroup: /system.slice/rsyslog.service
             └─372726 /usr/sbin/rsyslogd -n -iNONE

сеп 01 17:34:51 haproxy2 systemd[1]: Stopped System Logging Service.
сеп 01 17:34:51 haproxy2 rsyslogd[372726]: warning: ~ action is deprecated, consider using the 'stop' statement instead [v8.210>
сеп 01 17:34:51 haproxy2 systemd[1]: Starting System Logging Service…
сеп 01 17:34:51 haproxy2 rsyslogd[372726]: [198B blob data]
сеп 01 17:34:51 haproxy2 systemd[1]: Started System Logging Service.
сеп 01 17:34:51 haproxy2 rsyslogd[372726]: [198B blob data]
сеп 01 17:34:51 haproxy2 rsyslogd[372726]: [198B blob data]
сеп 01 17:34:51 haproxy2 rsyslogd[372726]: [198B blob data]
сеп 01 17:34:51 haproxy2 rsyslogd[372726]: imuxsock: Acquired UNIX socket '/run/systemd/journal/syslog' (fd 3) from systemd.  [>
сеп 01 17:34:51 haproxy2 rsyslogd[372726]: [origin software="rsyslogd" swVersion="8.2102.0" x-pid="372726" x-info="https://www.

Do some testing with some tool like curl / wget / lynx / elinks etc. on each of the configured haproxy listeners and frontends and check whether everything ends up in the correct log files.
That's all folks enjoy ! 🙂
 

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Posted in Hacks, Haproxy, Linux, Web and CMS | No Comments »

Zabbix: Monitor Linux rsyslog configured central log server is rechable with check_log_server_status.sh userparameter script

Wednesday, June 8th, 2022

zabbix-monitor-central-log-server-is-reachable-from-host-with-a-userparamater-script-zabbix-logo

On modern Linux OS servers on Redhat / CentOS / Fedora and Debian based distros log server service is usually running on the system  such as rsyslog (rsyslogd) to make sure the logging from services is properly logged in separate logs under /var/log.

A very common practice on critical server machines in terms of data security, where logs produced by rsyslog daermon needs to be copied over network via TCP or UDP protocol immediately is to copy over the /var/log produced logs to another configured central logging server. Then later every piece of bit generated by rsyslogd could be  overseen by a third party auditor person and useful for any investigation in case of logs integrity is required or at worse case if there is a suspicion that system in question is hacked by a malicious hax0r and logs have been "cleaned" up from any traces leading to the intruder (things usually done locally by hackers) or by any automated script exploit tools since yesr.

This doubled logging of system events to external log server  ipmentioned is very common practice by companies to protect their log data and quite useful for logs to be recovered easily later on from the central logging server machine that could be also setup for example to use rsyslogd to receive logs from other Linux machines in circumstances where some log disappears just like that (things i've seen happen) for any strange reason or gets destroyed by the admins mistake locally on machine / or by any other mean such as filesystem gets damaged. a very common practice by companies to protect their log data.  

Monitor remote logging server is reachable with userparameter script

Assuming that you already have setup a logging from the server hostname A towards the Central logging server log storepool and everything works as expected the next logical step is to have at least some basic way to monitor remote logging server configured is still reachable all the time and respectively rsyslog /var/log/*.* logs gets properly produced on remote side for example with something like a simple TCP remote server port check and reported in case of troubles in zabbix.

To solve that simple task for company where I'm employed, I've developed below check_log_server_status.sh:
 

#!/bin/bash
# @@ for TCP @ for UDP
# check_log_server_status.sh Script to check if configured TCP / UDP logging server in /etc/rsyslog.conf is rechable
# report to zabbix
DELIMITER='@@';
GREP_PORT='5145';
CONNECT_TIMEOUT=5;

PORT=$(grep -Ei "*.* $DELIMITER.*:$GREP_PORT" /etc/rsyslog.conf|awk -F : '{ print $2 }'|sort -rn |uniq);

#for i in $(grep -Ei "*.* $DELIMITER.*:$GREP_PORT" /etc/rsyslog.conf |grep -v '\#'|awk -F"$DELIMITER" '{ print $2 }' | awk -F ':' '{ print $1 }'|sort -rn); do
HOST=$(grep -Ei "*.* $DELIMITER.*:$GREP_PORT" /etc/rsyslog.conf |grep -v '\#'|awk -F"$DELIMITER" '{ print $2 }' | awk -F ':' '{ print $1 }'|sort -rn)

# echo $PORT

if [[ ! -z $PORT ]] && [[ ! -z $HOST ]]; then
SSH_RETURN=$(/bin/ssh $HOST -p $PORT -o ConnectTimeout=$CONNECT_TIMEOUT 2>&1);
else
echo "PROBLEM Port $GREP_PORT not defined in /etc/rsyslog.conf";
fi

##echo SSH_RETURN $SSH_RETURN;
#exit 1;
if [[ $(echo $SSH_RETURN |grep -i ‘Connection timed out during banner exchange’ | wc -l) -eq ‘1’ ]]; then
echo "rsyslogd $HOST:$PORT OK";
fi

if [[ $(echo $SSH_RETURN |grep -i ‘Connection refused’ | wc -l) -eq ‘1’ ]]; then
echo "rsyslogd $HOST:$PORT PROBLEM";
fi

#sleep 2;
#done


You can download a copy of the script check_log_server_status.sh here

Depending on the port the remote rsyslogd central logging server is using configure it in the script with respective port through the DELIMITER='@@', GREP_PORT='5145', CONNECT_TIMEOUT=5 values.

The delimiter is setup as usually in /etc/rsyslog.conf this the remote logging server for TCP IP is configured with @@ prefix to indicated TCP mode should be used.

Below is example from /etc/rsyslog.conf of how the rsyslogd server is configured:

[root@Server-hostA /root]# grep -i @@ /etc/rsyslogd.conf
# central remote Log server IP / port
*.* @@10.10.10.1:5145

To use the script on a machine, where you have a properly configured zabbix-agentd service host connected and reporting data to a zabbix-server monitoring server.

1. Set up the script under /usr/local/bin/check_log_server_status.sh

[root@Server-hostA /root ]# vim /usr/local/bin/check_log_server_status.sh
…

[root@Server-hostA /root ]# chmod +x /usr/local/bin/check_log_server_status.sh

2. Prepare userparameter_check_log_server.conf with log_server.check Item key

[root@Server-hostA zabbix_agentd.d]# cat userparameter_check_log_server.conf 
UserParameter=log_server.check, /usr/local/bin/check_log_server_status.sh

3. Set in Zabbix some Item such as on below screenshot

 

check-log-server-status-screenshot-linux-item-zabbix.png4. Create a Zabbix trigger 

check-log-server-status-trigger-logserver-is-unreachable-zabbix


The redded hided field in Expression field should be substituted with your actual hostname on which the monitor script will run.

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Posted in Monitoring, System Administration, Various, Zabbix | No Comments »

How to configure haproxy logging to separate file on Redhat Enterprise Linux 8.5 Ootpa

Thursday, February 3rd, 2022

haproxy-rsyslog-architecture-logging-picture

Configuring proper logging for haproxy is always a pain in the ass in Linux, because of rsyslogd various config syntax among versions, because of bugs in OS etc. 
Today we have been given 2 Redhat 8.5 Linux servers where we had a task to start configuring haproxies, to have an idea on what is going on of course we had to enable proper haproxy logging in separate log file under separate local, for the test one can use haproxy's 

log /dev/log local6

config, this is a general way to configure logging which I've described earlier in the article How to enable haproxy logging to a separate log /var/log/haproxy.log / prevent duplicate messages to appear in /var/log/messages
However this time I wanted to not use /dev/log as this device is also used by systemd / journald and theoretically could be used by other services and there might be multiple services logging to the same places possibly leading to some issue, thus I wanted to send and process the haproxy messages directly from rsyslog on RHEL 8.5.

Create a custom file that is loaded with the rest of configuration from /etc/rsyslog.conf with a line like:
 

# Include all config files in /etc/rsyslog.d/
include(file="/etc/rsyslog.d/*.conf" mode="optional")


Create 49_haproxy.conf with below content

[root@haproxy: ~]# vim /etc/rsyslog.d/49_haproxy.conf

$ModLoad imudp
$UDPServerAddress 127.0.0.1
$UDPServerRun 514
#2022/02/02: HAProxy logs to local6, save the messages
local6.*                                                /var/log/haproxy.log
if ($programname == 'haproxy') then -/var/log/haproxy.log
& stop

touch /var/log/haproxy.log
chown haproxy:haproxy /var/log/haproxy.log

In /etc/haproxy/haproxy.cfg under global section to print in verbose mode messages (i.e. check, the haproxy is receiving properly sent traffic) do configure something like:

 

global
  log          127.0.0.1 local6 debug


Eventually you might want to remove the debug word out of the config, if you don't want to log too much verbosily once everything is properly tested and configured

[root@haproxy: ~]# curl -v -c -k 10.10.192.135:16010
* Rebuilt URL to: 10.10.192.135:15010/
*   Trying 10.10.192.135…
* TCP_NODELAY set
* Connected to 10.10.192.135 (10.10.192.135) port 15010 (#0)
> GET / HTTP/1.1
> Host: 10.10.192.135:15010
> User-Agent: curl/7.61.1
> Accept: */*
> 
* Empty reply from server
* Connection #0 to host 10.10.192.135 left intact
curl: (52) Empty reply from server

 

In /var/log/haproxy.log you should get some messages like:
 

Feb  3 14:16:44 localhost.localdomain haproxy[25029]: proxy IN_Traffic_Bak has no server available!
Feb  3 14:16:44 localhost.localdomain haproxy[25029]: proxy IN_Traffic_Bak has no server available!
Feb  3 15:59:50 localhost.localdomain haproxy[25029]: [03/Feb/2022:15:59:50.162] 10.44.192.135:1348 -:- IN_Traffic/<NOSRV>:- -1/-1/0 0 SC 1/1/0/0/0 0/0
Feb  3 15:59:50 localhost.localdomain haproxy[25029]: [03/Feb/2022:15:59:50.162] 10.44.192.135:1348 -:- IN_Traffic/<NOSRV>:- -1/-1/0 0 SC 1/1/0/0/0 0/0
Feb  3 15:59:50 localhost.localdomain haproxy[25029]: [03/Feb/2022:15:59:50.162] 10.44.192.135:1348 -:- IN_Traffic/<NOSRV>:- -1/-1/0 0 SC 1/1/0/0/0 0/0

 

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Log rsyslog script incoming tagged string message to separate external file to prevent /var/log/message from string flood

Wednesday, December 22nd, 2021

rsyslog_logo-log-external-tag-scripped-messages-to-external-file-linux-howto

If you're using some external bash script to log messages via rsyslogd to some of the multiple rsyslog understood data tubes (called in rsyslog language facility levels) and you want Rsyslog to move message string to external log file, then you had the same task as me few days ago.

For example you have a bash shell script that is writting a message to rsyslog daemon to some of the predefined facility levels be it:
 

kern,user,cron, auth etc. or some local

and your logged script data ends under the wrong file location /var/log/messages , /var/log/secure , var/log/cron etc. However  you need to log everything coming from that service to a separate file based on the localX (fac. level) the usual way to do it is via some config like, as you would usually do it with rsyslog variables as:
 

local1.info                                            /var/log/custom-log.log

# Don't log private authentication messages!
*.info;mail.none;authpriv.none;cron.none;local0.none;local1.none        /var/log/messages


Note the local1.none is instructing the rsyslog not to log anything from local1 facility towards /var/log/message. 
But what if this due to some weirdness in configuration of rsyslog on the server or even due to some weird misconfiguration in

/etc/systemd/journald.conf such as:

[Journal]
Storage=persistent
RateLimitInterval=0s
RateLimitBurst=0
SystemMaxUse=128M
SystemMaxFileSize=32M
MaxRetentionSec=1month
MaxFileSec=1week
ForwardToSyslog=yes
SplitFiles=none

Due to that config and especially the FowardToSyslog=yes, the messages sent via the logger tool to local1 still end up inside /var/log/messages, not nice huh ..

The result out of that is anything being sent with a predefined TAGGED string via the whatever.sh script which uses the logger command  (if you never use it check man logger) to enter message into rsyslog with cmd like:
 

# logger -p local1.info -t TAG_STRING

# logger -p local2.warn test
# tail -2 /var/log/messages
Dec 22 18:58:23 pcfreak rsyslogd: — MARK —
Dec 22 19:07:12 pcfreak hipo: test


was nevertheless logged to /var/log/message.
Of course /var/log/message becomes so overfilled with "junk" shell script data not related to real basic Operating system adminsitration, so this prevented any critical or important messages that usually should come under /var/log/message / /var/log/syslog to be lost among the big quantities of other tagged tata reaching the log.

After many attempts to resolve the issue by modifying /etc/rsyslog.conf as well as the messed /etc/systemd/journald.conf (which by the way was generated with this strange values with an OS install time automation ansible stuff). It took me a while until I found the solution on how to tell rsyslog to log the tagged message strings into an external separate file. From my 20 minutes of research online I have seen multitudes of people in different Linux OS versions to experience the same or similar issues due to whatever, thus this triggered me to write this small article on the solution to rsyslog.

The solution turned to be pretty easy but requires some further digging into rsyslog, Redhat's basic configuration on rsyslog documentation is a very nice reading for starters, in my case I've used one of the Propery-based compare-operations variable contains used to select my tagged message string.
 

1. Add msg contains compare-operations to output log file and discard the messages

[root@centos bin]# vi /etc/rsyslog.conf

# config to log everything logged to rsyslog to a separate file
:msg, contains, "tag_string:/"         /var/log/custom-script-log.log
:msg, contains, "tag_string:/"    ~

Substitute quoted tag_string:/ to whatever your tag is and mind that it is better this config is better to be placed somewhere near the beginning of /etc/rsyslog.conf and touch the file /var/log/custom-script-log.log and give it some decent permissions such as 755, i.e.
 

1.1 Discarding a message


The tilda sign –  ~ 

as placed to the end of the msg, contains is the actual one to tell the string to be discarded so it did not end in /var/log/messages.

Alternative rsyslog config to do discard the unwanted message once you have it logged is with the
rawmsg variable, like so:

 

# config to log everything logged to rsyslog to a separate file
:msg, contains, "tag_string:/"         /var/log/custom-script-log.log
:rawmsg, isequal, "tag_string:/" stop

Other way to stop logging immediately after log is written to custom file across some older versions of rsyslog is via the &stop

:msg, contains, "tag_string:/"         /var/log/custom-script-log.log
& stop

I don't know about other versions but Unfortunately the &stop does not work on RHEL 7.9 with installed rpm package rsyslog-8.24.0-57.el7_9.1.x86_64.

1.2 More with property based filters basic exclusion of string 

Property based filters can do much more, you can for example, do regular expression based matches of strings coming to rsyslog and forward to somewhere.

To select syslog messages which do not contain any mention of the words fatal and error with any or no text between them (for example, fatal lib error), type:

:msg, !regex, "fatal .* error"

 

2. Create file where tagged data should be logged and set proper permissions
 

[root@centos bin]# touch /var/log/custom-script-log.log
[root@centos bin]# chmod 755 /var/log/custom-script-log.log


3. Test rsyslogd configuration for errors and reload rsyslog

[root@centos ]# rsyslogd -N1
rsyslogd: version 8.24.0-57.el7_9.1, config validation run (level 1), master config /etc/rsyslog.conf
rsyslogd: End of config validation run. Bye.
[root@centos ]# systemctl restart rsyslog
[root@centos ]#  systemctl status rsyslog 
● rsyslog.service – System Logging Service
   Loaded: loaded (/usr/lib/systemd/system/rsyslog.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2021-12-22 13:40:11 CET; 3h 5min ago
     Docs: man:rsyslogd(8)
           http://www.rsyslog.com/doc/
 Main PID: 108600 (rsyslogd)
   CGroup: /system.slice/rsyslog.service
           └─108600 /usr/sbin/rsyslogd -n

 

4. Property-based compare-operations supported by rsyslog table
 

Compare-operation Description
contains Checks whether the provided string matches any part of the text provided by the property. To perform case-insensitive comparisons, use  contains_i .
isequal Compares the provided string against all of the text provided by the property. These two values must be exactly equal to match.
startswith Checks whether the provided string is found exactly at the beginning of the text provided by the property. To perform case-insensitive comparisons, use  startswith_i .
regex Compares the provided POSIX BRE (Basic Regular Expression) against the text provided by the property.
ereregex Compares the provided POSIX ERE (Extended Regular Expression) regular expression against the text provided by the property.
isempty Checks if the property is empty. The value is discarded. This is especially useful when working with normalized data, where some fields may be populated based on normalization result.

 


5. Rsyslog understanding Facility levels

Here is a list of facility levels that can be used.

Note: The mapping between Facility Number and Keyword is not uniform over different operating systems and different syslog implementations, so among separate Linuxes there might be diference in the naming and numbering.

Facility Number Keyword Facility Description
0 kern kernel messages
1 user user-level messages
2 mail mail system
3 daemon system daemons
4 auth security/authorization messages
5 syslog messages generated internally by syslogd
6 lpr line printer subsystem
7 news network news subsystem
8 uucp UUCP subsystem
9   clock daemon
10 authpriv security/authorization messages
11 ftp FTP daemon
12 – NTP subsystem
13 – log audit
14 – log alert
15 cron clock daemon
16 local0 local use 0 (local0)
17 local1 local use 1 (local1)
18 local2 local use 2 (local2)
19 local3 local use 3 (local3)
20 local4 local use 4 (local4)
21 local5 local use 5 (local5)
22 local6 local use 6 (local6)
23 local7 local use 7 (local7)


6. rsyslog Severity levels (sublevels) accepted by facility level

As defined in RFC 5424, there are eight severity levels as of year 2021:

Code Severity Keyword Description General Description
0 Emergency emerg (panic) System is unusable. A "panic" condition usually affecting multiple apps/servers/sites. At this level it would usually notify all tech staff on call.
1 Alert alert Action must be taken immediately. Should be corrected immediately, therefore notify staff who can fix the problem. An example would be the loss of a primary ISP connection.
2 Critical crit Critical conditions. Should be corrected immediately, but indicates failure in a primary system, an example is a loss of a backup ISP connection.
3 Error err (error) Error conditions. Non-urgent failures, these should be relayed to developers or admins; each item must be resolved within a given time.
4 Warning warning (warn) Warning conditions. Warning messages, not an error, but indication that an error will occur if action is not taken, e.g. file system 85% full – each item must be resolved within a given time.
5 Notice notice Normal but significant condition. Events that are unusual but not error conditions – might be summarized in an email to developers or admins to spot potential problems – no immediate action required.
6 Informational info Informational messages. Normal operational messages – may be harvested for reporting, measuring throughput, etc. – no action required.
7 Debug debug Debug-level messages. Info useful to developers for debugging the application, not useful during operations.


7. Sample well tuned configuration using severity and facility levels and immark, imuxsock, impstats
 

Below is sample config using severity and facility levels
 

# Don't log private authentication messages!
*.info;mail.none;authpriv.none;cron.none;local0.none;local1.none        /var/log/messages


Note the local0.none; local1.none tells rsyslog to not log from that facility level to /var/log/messages.

If you need a complete set of rsyslog configuration fine tuned to have a proper logging with increased queues and included configuration for loggint to remote log aggegator service as well as other measures to prevent the system disk from being filled in case if something goes wild with a logging service leading to a repeatedly messages you might always contact me and I can help 🙂
 Other from that sysadmins might benefit from a sample set of configuration prepared with the Automated rsyslog config builder  or use some fine tuned config  for rsyslog-8.24.0-57.el7_9.1.x86_64 on Redhat 7.9 (Maipo)   rsyslog_config_redhat-2021.tar.gz.

To sum it up rsyslog though looks simple and not an important thing to pre

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Set all logs to log to to physical console /dev/tty12 (tty12) on Linux

Wednesday, August 12th, 2020

tty linux-logo how to log everything to last console terminal tty12

Those who administer servers from the days of birth of Linux and who used actively GNU / Linux over the years or any other UNIX knows how practical could be to configure logging of all running services / kernel messages / errors and warnings on a physical console.

Traditionally from the days I was learning Linux basics I was shown how to do this on an old Debian Sarge 3.0 Linux without systemd and on all Linux distributions Redhat 9.0 / Calderas and Mandrakes I've used either as a home systems or for servers. I've always configured output of all messages to go to the last easy to access console /dev/tty12 (for those who never use it console switching under Linux plain text console mode is done with key combination of CTRL + ALT + F1 .. F12.

In recent times however with the introduction of systemd pretty much things changed as messages to console are not handled by /etc/inittab which was used to add and refresh physical consoles tty1, tty2 … tty7 (the default added one on Linux were usually 7), but I had to manually include more respawn lines for each console in /etc/inittab.
Nowadays as of year 2020 Linux distros /etc/inittab is no longer there being obsoleted and console print out of INPUT / OUTPUT messages are handled by systemd.
 

1. Enable Physical TTYs from TTY8 till TTY12 etc.


The number of default consoles existing in most Linux distributions I've seen is still from tty1 to tty7. Hence to add more tty consoles and be ready to be able to switch out  not only towards tty7 but towards tty12 once you're connected to the server via a remote ILO (Integrated Lights Out) / IdRAC (Dell Remote Access Controller) / IPMI / IMM (Imtegrated Management Module), you have to do it by telling systemd issuing below systemctl commands:
 

 

 # systemctl enable getty@tty8.service Created symlink /etc/systemd/system/getty.target.wants/getty@tty8.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty9.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty9.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty10.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty10.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty11.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty11.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty12.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty12.service -> /lib/systemd/system/getty@.service.


Once the TTYS tty7 to tty12 are enabled you will be able to switch to this consoles either if you have a physical LCD / CRT monitor or KVM switch connected to the machine mounted on the Rack shelf once you're in the Data Center or will be able to see it once connected remotely via the Management IP Interface (ILO) remote console.
 

2. Taking screenshot of the physical console TTY with fbcat


For example below is a screenshot of the 10th enabled tty10:

tty10-linux-screenshot-fbcat-how-to-screenshot-console

As you can in the screenshot I've used the nice tool fbcat that can be used to make a screenshot of remote console. This is very useful especially if remote access via a SSH client such as PuTTY / MobaXterm is not there but you have only a physical attached monitor access on a DCs that are under a heavy firewall that is preventing anyone to get to the system remotely. For example screenshotting the physical console in case if there is a major hardware failure occurs and you need to dump a hardware error message to a flash drive that will be used to later be handled to technicians to analyize it and exchange the broken server hardware part.

Screenshots of the CLI with fbcat is possible across most Linux distributions where as usual.

In Debian you have to first instal the tool via :
 

# apt install –yes fbcat
…


and on RedHats / CentOS / Fedoras

# yum install -y fbcat
…


Taking screenshot once tool is on the server of whatever you have printed on console is as easy as

# fbcat > tty_name.ppm


Note that you might want to convert the .ppm created picture to png with any converter such as imagemagick's convert command or if you have a GUI perhaps with GNU Image Manipulation Tool (GIMP).

3. Enabling every rsyslog handled message to log to Physical TTY12


To make everything such as errors, notices, debug, warning messages  become instantly logging towards above added new /dev/tty12.

Open /etc/rsyslog.conf and to the end of the file append below line :
 

daemon,mail.*;\
   news.=crit;news.=err;news.=notice;\
   *.=debug;*.=info;\
   *.=notice;*.=warn   /dev/tty12


To make rsyslog load its new config restart it:

 

# systemctl status rsyslog

 

 

 

● rsyslog.service – System Logging Service
   Loaded: loaded (/lib/systemd/system/rsyslog.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2020-08-10 04:09:36 EEST; 2 days ago
     Docs: man:rsyslogd(8)
           https://www.rsyslog.com/doc/
 Main PID: 671 (rsyslogd)
    Tasks: 4 (limit: 4915)
   Memory: 12.5M
   CGroup: /system.slice/rsyslog.service
           └─671 /usr/sbin/rsyslogd -n -iNONE

 

авг 12 00:00:05 pcfreak rsyslogd[671]:  [origin software="rsyslogd" swVersion="8.1901.0" x-pid="671" x-info="https://www.rsyslo
Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.

 

#  systemctl restart rsyslog


That's all folks navigate by pressing simultaneously CTRL + ALT + F12 to get to TTY12 or use ALT + LEFT / ALT + RIGHT ARROW (console switch commands) till you get to the console where everything should be now logged.

Enjoy and if you like this article share to tell your sysadmin friends about this nice hack  ! 🙂

 

 

 

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