Posts Tagged ‘servers’

« Older Entries
Newer Entries »

How to completely disable Replication in MySQL server 5.1.61 on Debian GNU / Linux

Monday, July 16th, 2012

Replication_mysql_disable

Some time ago on one of the Database MySQL servers, I've configured replication as it was required to test somethings. Eventually it turned out replication will be not used (for some reason) it was too slow and not fitting our company needs hence we needed to disable it.

It seemed logical to me that, simply removing any replication related directives from my.cnf and a restart of the SQL server will be enough to turn replication off on the Debian Linux host. Therefore I proceeded removed all replication configs from /etc/my/my.cnf and issued MySQL restart i. e.:

sql-server:~# /etc/init.d/mysql restart
....

This however didn't turned off replication,as I thought and in phpmyadminweb frontend interface, replication was still appearing to be active in the replication tab.

Something was still making the SQL server still act as an Replication Slave Host, so after a bit of pondering and trying to remember, the exact steps I took to make the replication work on the host I remembered that actually I issued:

mysql> START SLAVE;

Onwards I run:

mysql> SHOW SLAVE STATUS;
....

and found in the database the server was still running in Slave Replication mode

Hence to turn off the db host run as a Slave, I had to issue in mysql cli:

mysql> STOP SLAVE;
Query OK, 0 rows affected, 1 warning (0.01 sec)
mysql> RESET SLAVE;
Query OK, 0 rows affected, 1 warning (0.01 sec)

Then after a reload of SQL server in memory, the host finally stopped working as a Slave Replication host, e.g.

sql-server:~# /etc/init.d/mysql restart
....

After the restart, to re-assure myself the SQL server is no more set to run as MySQL replication Slave host:

mysql> SHOW SLAVE STATUS;
Empty set (0.00 sec)

Cheers 😉

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,
Posted in MySQL, System Administration | 1 Comment »

WordPress Security: Fix WordPress wp-config.php improper permissions to protect your sites from Database password steal / Website deface

Thursday, March 12th, 2015

wordpress-security-Fix-wordpress-wp-config-improper-permissions-to-protect-your-sites-from-Database-pass-steal
Keeping WordPress Site / Blog and related installed plugins up-to-date is essential to prevent an attacker to hack into your Site / Database and deface your site, however if you're a company providing shell access from Cpanel / Plesk / Kloxo Panel to customers often customers are messing up permissions leaving important security credential files such as wp-config.php (which is storing user / pass credentials about connection to MySQL / PostgreSQL to have improper permissions and be world readable e.g. have permissions such as 666 or 777 while in reality the WordPress recommended permissions for wp-config.php is 600. I will skip here to explain in details difference between file permissions on Linux as this is already well described in any Linux book, however I just will recommend for any Share hosting Admin where Wordperss is hosted on Lighttpd / Apache Webserver + Some kind of backend database to be extra cautious.

Hence it is very useful to list all your WordPress sites on server wp-config.php permissions with find like this:

 

find /  -iname 'wp-config.php' -print1;

 

I find it a generally good practice to also automatically set all wp-config.php permissions to 600 (6= Read / Write  permissions only for File Owner  user 0 = No permissions for All groups, 0 = No Permissions for all non-owner users)

If find command output gives you some file permissions such as:
 

ls -al /var/www/wordpress-bak/wp-config.php
-rw-rw-rw- 1 www-data www-data 2654 jul 28  2009 wp-config.php

 

E.g. file permission has 666 permissions (Readable for all users), then it is wise to fix this with:
 

chmod 600 /var/www/wordpress-bak/wp-config.php


It is generally a very good practice to run also a chmod 600 to each and every found wp-config.php file on server:
 

find /  -iname 'wp-config.php' -print1 -exec chmod 600 '{}' \;


Above command will also print each file to whcih permission is set to Read / Write for Owner (this si done with -print1 option).

It is a good practice for shared hosting server to always configure a root cronjob to run above find chmod command at least once daily (whenever server hosts 50 – 100 wordpress+ more sites).
 

crontab -u root -l | { cat; echo “05 03 * * * find /  -iname 'wp-config.php' -print1 -exec chmod 600 '{}' \; } | crontab – 


If you don't have the 600 permissions set for all wp-config.php files this security "backdoor" can be used by any existing non-root user to be read and to break up (crack)  in your database and even when there are Deface bot-nets involved to deface all your hosted server wordpress sites.

One of my servers with wordpress has just recently suffered with this little but very important security hole due to a WordPress site directory backup  with improper permissions which allowed anyone to enter MySQL database, so I guess there are plenty of servers with this hidden vulnerability silently living.

Many thanks to my dear friend (Dimitar Paskalev) Nomen for sharing with me about this vulnerability! Very important note to make here is admins who are using some security enhancement modules such as SuPHP (which makes Apache webserver to run Separate Website instances with different user), should be careful with his set all wp-config.php modules to Owner, as it is possible the wp-config.php owner change to make customer WP based websites inaccessible.

Another good security measure to  protect your server WordPress based sites from malicious theme template injections (for both personal own hosted wordpress based blog / sites or a WordPress hosting company) is to install and activate WordPress Antivirus plugin.

Tags: , , , , , , , , , , , , , , , , ,
Posted in Computer Security, Linux, System Administration, Web and CMS, Wordpress | No Comments »

Resolving “nf_conntrack: table full, dropping packet.” flood message in dmesg Linux kernel log

Wednesday, March 28th, 2012

nf_conntrack_table_full_dropping_packet
On many busy servers, you might encounter in /var/log/syslog or dmesg kernel log messages like

nf_conntrack: table full, dropping packet

to appear repeatingly:

[1737157.057528] nf_conntrack: table full, dropping packet.
[1737157.160357] nf_conntrack: table full, dropping packet.
[1737157.260534] nf_conntrack: table full, dropping packet.
[1737157.361837] nf_conntrack: table full, dropping packet.
[1737157.462305] nf_conntrack: table full, dropping packet.
[1737157.564270] nf_conntrack: table full, dropping packet.
[1737157.666836] nf_conntrack: table full, dropping packet.
[1737157.767348] nf_conntrack: table full, dropping packet.
[1737157.868338] nf_conntrack: table full, dropping packet.
[1737157.969828] nf_conntrack: table full, dropping packet.
[1737157.969928] nf_conntrack: table full, dropping packet
[1737157.989828] nf_conntrack: table full, dropping packet
[1737162.214084] __ratelimit: 83 callbacks suppressed

There are two type of servers, I've encountered this message on:

1. Xen OpenVZ / VPS (Virtual Private Servers)
2. ISPs – Internet Providers with heavy traffic NAT network routers
 

I. What is the meaning of nf_conntrack: table full dropping packet error message

In short, this message is received because the nf_conntrack kernel maximum number assigned value gets reached.
The common reason for that is a heavy traffic passing by the server or very often a DoS or DDoS (Distributed Denial of Service) attack. Sometimes encountering the err is a result of a bad server planning (incorrect data about expected traffic load by a company/companeis) or simply a sys admin error…

– Checking the current maximum nf_conntrack value assigned on host:

linux:~# cat /proc/sys/net/ipv4/netfilter/ip_conntrack_max
65536

– Alternative way to check the current kernel values for nf_conntrack is through:

linux:~# /sbin/sysctl -a|grep -i nf_conntrack_max
error: permission denied on key 'net.ipv4.route.flush'
net.netfilter.nf_conntrack_max = 65536
error: permission denied on key 'net.ipv6.route.flush'
net.nf_conntrack_max = 65536

– Check the current sysctl nf_conntrack active connections

To check present connection tracking opened on a system:

:

linux:~# /sbin/sysctl net.netfilter.nf_conntrack_count
net.netfilter.nf_conntrack_count = 12742

The shown connections are assigned dynamicly on each new succesful TCP / IP NAT-ted connection. Btw, on a systems that work normally without the dmesg log being flooded with the message, the output of lsmod is:

linux:~# /sbin/lsmod | egrep 'ip_tables|conntrack'
ip_tables 9899 1 iptable_filter
x_tables 14175 1 ip_tables

On servers which are encountering nf_conntrack: table full, dropping packet error, you can see, when issuing lsmod, extra modules related to nf_conntrack are shown as loaded:

linux:~# /sbin/lsmod | egrep 'ip_tables|conntrack'
nf_conntrack_ipv4 10346 3 iptable_nat,nf_nat
nf_conntrack 60975 4 ipt_MASQUERADE,iptable_nat,nf_nat,nf_conntrack_ipv4
nf_defrag_ipv4 1073 1 nf_conntrack_ipv4
ip_tables 9899 2 iptable_nat,iptable_filter
x_tables 14175 3 ipt_MASQUERADE,iptable_nat,ip_tables

 

II. Remove completely nf_conntrack support if it is not really necessery

It is a good practice to limit or try to omit completely use of any iptables NAT rules to prevent yourself from ending with flooding your kernel log with the messages and respectively stop your system from dropping connections.

Another option is to completely remove any modules related to nf_conntrack, iptables_nat and nf_nat.
To remove nf_conntrack support from the Linux kernel, if for instance the system is not used for Network Address Translation use:

/sbin/rmmod iptable_nat
/sbin/rmmod ipt_MASQUERADE
/sbin/rmmod rmmod nf_nat
/sbin/rmmod rmmod nf_conntrack_ipv4
/sbin/rmmod nf_conntrack
/sbin/rmmod nf_defrag_ipv4

Once the modules are removed, be sure to not use iptables -t nat .. rules. Even attempt to list, if there are any NAT related rules with iptables -t nat -L -n will force the kernel to load the nf_conntrack modules again.

Btw nf_conntrack: table full, dropping packet. message is observable across all GNU / Linux distributions, so this is not some kind of local distribution bug or Linux kernel (distro) customization.
 

III. Fixing the nf_conntrack … dropping packets error

– One temporary, fix if you need to keep your iptables NAT rules is:

linux:~# sysctl -w net.netfilter.nf_conntrack_max=131072

I say temporary, because raising the nf_conntrack_max doesn't guarantee, things will get smoothly from now on.
However on many not so heavily traffic loaded servers just raising the net.netfilter.nf_conntrack_max=131072 to a high enough value will be enough to resolve the hassle.

– Increasing the size of nf_conntrack hash-table

The Hash table hashsize value, which stores lists of conntrack-entries should be increased propertionally, whenever net.netfilter.nf_conntrack_max is raised.

linux:~# echo 32768 > /sys/module/nf_conntrack/parameters/hashsize
The rule to calculate the right value to set is:
hashsize = nf_conntrack_max / 4

– To permanently store the made changes ;a) put into /etc/sysctl.conf:

linux:~# echo 'net.netfilter.nf_conntrack_count = 131072' >> /etc/sysctl.conf
linux:~# /sbin/sysct -p

b) put in /etc/rc.local (before the exit 0 line):

echo 32768 > /sys/module/nf_conntrack/parameters/hashsize

Note: Be careful with this variable, according to my experience raising it to too high value (especially on XEN patched kernels) could freeze the system.
Also raising the value to a too high number can freeze a regular Linux server running on old hardware.

– For the diagnosis of nf_conntrack stuff there is ;

/proc/sys/net/netfilter kernel memory stored directory. There you can find some values dynamically stored which gives info concerning nf_conntrack operations in "real time":

linux:~# cd /proc/sys/net/netfilter
linux:/proc/sys/net/netfilter# ls -al nf_log/
total 0
dr-xr-xr-x 0 root root 0 Mar 23 23:02 ./
dr-xr-xr-x 0 root root 0 Mar 23 23:02 ../
-rw-r--r-- 1 root root 0 Mar 23 23:02 0
-rw-r--r-- 1 root root 0 Mar 23 23:02 1
-rw-r--r-- 1 root root 0 Mar 23 23:02 10
-rw-r--r-- 1 root root 0 Mar 23 23:02 11
-rw-r--r-- 1 root root 0 Mar 23 23:02 12
-rw-r--r-- 1 root root 0 Mar 23 23:02 2
-rw-r--r-- 1 root root 0 Mar 23 23:02 3
-rw-r--r-- 1 root root 0 Mar 23 23:02 4
-rw-r--r-- 1 root root 0 Mar 23 23:02 5
-rw-r--r-- 1 root root 0 Mar 23 23:02 6
-rw-r--r-- 1 root root 0 Mar 23 23:02 7
-rw-r--r-- 1 root root 0 Mar 23 23:02 8
-rw-r--r-- 1 root root 0 Mar 23 23:02 9

 

IV. Decreasing other nf_conntrack NAT time-out values to prevent server against DoS attacks

Generally, the default value for nf_conntrack_* time-outs are (unnecessery) large.
Therefore, for large flows of traffic even if you increase nf_conntrack_max, still shorty you can get a nf_conntrack overflow table resulting in dropping server connections. To make this not happen, check and decrease the other nf_conntrack timeout connection tracking values:

linux:~# sysctl -a | grep conntrack | grep timeout
net.netfilter.nf_conntrack_generic_timeout = 600
net.netfilter.nf_conntrack_tcp_timeout_syn_sent = 120
net.netfilter.nf_conntrack_tcp_timeout_syn_recv = 60
net.netfilter.nf_conntrack_tcp_timeout_established = 432000
net.netfilter.nf_conntrack_tcp_timeout_fin_wait = 120
net.netfilter.nf_conntrack_tcp_timeout_close_wait = 60
net.netfilter.nf_conntrack_tcp_timeout_last_ack = 30
net.netfilter.nf_conntrack_tcp_timeout_time_wait = 120
net.netfilter.nf_conntrack_tcp_timeout_close = 10
net.netfilter.nf_conntrack_tcp_timeout_max_retrans = 300
net.netfilter.nf_conntrack_tcp_timeout_unacknowledged = 300
net.netfilter.nf_conntrack_udp_timeout = 30
net.netfilter.nf_conntrack_udp_timeout_stream = 180
net.netfilter.nf_conntrack_icmp_timeout = 30
net.netfilter.nf_conntrack_events_retry_timeout = 15
net.ipv4.netfilter.ip_conntrack_generic_timeout = 600
net.ipv4.netfilter.ip_conntrack_tcp_timeout_syn_sent = 120
net.ipv4.netfilter.ip_conntrack_tcp_timeout_syn_sent2 = 120
net.ipv4.netfilter.ip_conntrack_tcp_timeout_syn_recv = 60
net.ipv4.netfilter.ip_conntrack_tcp_timeout_established = 432000
net.ipv4.netfilter.ip_conntrack_tcp_timeout_fin_wait = 120
net.ipv4.netfilter.ip_conntrack_tcp_timeout_close_wait = 60
net.ipv4.netfilter.ip_conntrack_tcp_timeout_last_ack = 30
net.ipv4.netfilter.ip_conntrack_tcp_timeout_time_wait = 120
net.ipv4.netfilter.ip_conntrack_tcp_timeout_close = 10
net.ipv4.netfilter.ip_conntrack_tcp_timeout_max_retrans = 300
net.ipv4.netfilter.ip_conntrack_udp_timeout = 30
net.ipv4.netfilter.ip_conntrack_udp_timeout_stream = 180
net.ipv4.netfilter.ip_conntrack_icmp_timeout = 30

All the timeouts are in seconds. net.netfilter.nf_conntrack_generic_timeout as you see is quite high – 600 secs = (10 minutes).
This kind of value means any NAT-ted connection not responding can stay hanging for 10 minutes!

The value net.netfilter.nf_conntrack_tcp_timeout_established = 432000 is quite high too (5 days!)
If this values, are not lowered the server will be an easy target for anyone who would like to flood it with excessive connections, once this happens the server will quick reach even the raised up value for net.nf_conntrack_max and the initial connection dropping will re-occur again …

With all said, to prevent the server from malicious users, situated behind the NAT plaguing you with Denial of Service attacks:

Lower net.ipv4.netfilter.ip_conntrack_generic_timeout to 60 – 120 seconds and net.ipv4.netfilter.ip_conntrack_tcp_timeout_established to stmh. like 54000

linux:~# sysctl -w net.ipv4.netfilter.ip_conntrack_generic_timeout = 120
linux:~# sysctl -w net.ipv4.netfilter.ip_conntrack_tcp_timeout_established = 54000

This timeout should work fine on the router without creating interruptions for regular NAT users. After changing the values and monitoring for at least few days make the changes permanent by adding them to /etc/sysctl.conf

linux:~# echo 'net.ipv4.netfilter.ip_conntrack_generic_timeout = 120' >> /etc/sysctl.conf
linux:~# echo 'net.ipv4.netfilter.ip_conntrack_tcp_timeout_established = 54000' >> /etc/sysctl.conf

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,
Posted in Computer Security, Linux, Networking, System Administration, Virtual Machines | 10 Comments »

Speed up WordPress / Joomla CMS and MySQL server on Linux with tmpfs ram file system / Decrease Website pageload times with RAM caching

Wednesday, March 4th, 2015

speed-up-accelerate-wordpress-joomla-drupal-cms-and-mysql-server-with-tmpfs_ramfs_decrease-pageload-times-with-ram-caching
As a WordPress blog owner and an sys admin that has to deal with servers running a lot of WordPress / Joomla / Droopal and other custom CMS installed on servers, performoing slow or big enough to put a significant load on servers and I love efficiency and hardware cost saving is essential for my daily job, I'm constantly trying to find new ways to optimize Customer Website (WordPress) and rest of sites in order to utilize better our servers and improve our clients sites speed (and hence satisfaction). 

There is plenty of little things to do on servers but probably among the most crucial ones which we use nowadays that save us a lot of money is tmpfs, and earlier (ramfs) – previously known as shmfs).
TMPFS is a (Temporary File Storage Facility) Linux kernel technology based on ramfs (used by Linux kernel initrd / initramfs on boot time in order to load and store the Linux kernel in memory, before system hard disk partition file systems are mounted) which is heavily used by virtually all modern popular Linux distributions. 

Using ramfs (cramfs variation – Compressed ROM filesystem) has been used to store different system environment kernel and Desktop components of many Linux environment / applications and used by a lot of the Linux BootCD such as the most famous (Klaus Knopper's) KNOPPIX LiveCD and Trinity Rescue Kit Linux (TRK uses /dev/shm which btw can be seen on most modern Linux distros and is actually just another mounted tmpfs).
If you haven't tried Live Linux yet try it out as me and a lot of sysadmins out there use some kind of LiveLinux at least few times on yearly basis  to Recover Unbootable Linux servers after some applied remote Updates as well as for Rescuing (Save) Data from Linux server failing to properly boot because of hard disk (bad blocks) failures. As I said earlier TMPFS is also used on almost any distribution for the /dev/ filesystem which is kept in memory.

You can see which tmpfs partitions is used on your Linux server with:

 

debian-server:~# mount |grep -i tmpfs
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)

 

Above is an output from a standard Debian Linux server. On CentOS 7 standard mounted tmpfs are as follows:

 

[root@centos ~]# mount |grep -i tmpfs
devtmpfs on /dev type devtmpfs (rw,nosuid,seclabel,size=1016332k,nr_inodes=254083,mode=755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,seclabel)
tmpfs on /run type tmpfs (rw,nosuid,nodev,seclabel,mode=755)
tmpfs on /sys/fs/cgroup type tmpfs (rw,nosuid,nodev,noexec,seclabel,mode=755)

 

[root@centos ~]# df -h|grep -i tmpfs
devtmpfs                 993M     0  993M   0% /dev
tmpfs                   1002M   92K 1002M   1% /dev/shm
tmpfs                   1002M  8.8M  993M   1% /run
tmpfs                   1002M     0 1002M   0% /sys/fs/cgroup

The /run tmpfs mounted directory is also to be seen also on latest Ubuntus and Fedoras and is actually the good old /var/run ( where applications keep there pids and some small app related files) stored in tmpfs filesystem stored in memory.

If you're wondering what is /dev/shm and why it appears mounted on every single Linux Server / Desktop you've ever used this is a special filesystem shared memory which various running programs (processes) can use to transfer data quick and efficient between each other to preven the slow disk swapping. People using Linux for the rest 15 years should remember /dev/shm has been a target of a lot of kernel exploits as historically it had a lot of security issues.

While writting this article I've just checked about KNOPPIX developed amd just for info as of time of writting this distro has already 1000+ programs on CD version and 2600+ packages / application on DVD version.
Nowadays Knoppix is mostly used mostly as USB Live Flash drive as a lot of people are dropping CD / DVD use (many servers doesn't have a CD / DVD Drive) and for USB Live Flash Linux distros tmpfs is also key technology used as this gives the end user an amazing fast experience (Desktop applications run much fasten on Live USBs when tmpfs is used than when the slow 7200 RPM HDDs are used).

Loading big parts of the distribution within RAM (with tmpfs from Linux Kernel 2.4+ onwards) is also heavily used by a lot of Cluster vendors in most of Clustered (Cloud) Linux based environemnts, cause TMPFS gives often speeds up improvements to x30 times and decreases greatly I/O HDD. FreeBSD users will be happy to know that TMPFS is already ported and could be used on from FreeBSD 7.0+ onward.

In this small article I will give you example use on how I use tmpfs to speed up our WordPress Websites which use WP Caching plugins such as W3 Total Cache and WP Super Cache
and Hyper Cache / WP Super Cache disk caching and MySQL server as a Database backend. Below example is wordpress specific but since it can be easily applied to Joomla, Drupal or any other CMS out there that uses mySQL server to make a lot of CPU expensive memory hungry (LEFT JOIN) queries which end up using a slow 7200 RPM hard disk.


 

1. Preparing tmpfs partitions for WordPress File Cache directory
 

If you want to give tmpfs a test drive, I recommend you try to create / mount a 20 Megabyte partition. To create a tmpfs partition you don't need to use a tool like mkfs.ext3 / mkfs.ext4 as TMPFS is in reality a virtual filesystem that is mapped in the server system physical RAM (volatile memory). TMPFS is very nice because if you run out of free RAM system starts a combination of RAM use + some Hard disk SWAP 
The great thing about TMPFS is it never uses all of the available RAM and SWAP, which would not halt your server if TMPFS partition gets filled, but instead you will start getting the usual "Insufficient Disk Space", just like with a physical HDD parititon. RAMFS cares much less about server compared to TMPFS, because if RAMFS is historically older.

ramfs file systems cannot be limited in size like a disk base file system which is limited by it’s capacity, thus ramfs will continue using memory storage until the system runs out of RAM and likely crashes or becomes unresponsive. This is a problem if the application writing to the file system cannot be limited in total size, so in my opinion you better stay away from RAMFS except you have a good idea what you're doing. Another disadvantage of RAMFS compared to TMPFS is you cannot see the size of the file system in df and it can only be estimated by looking at the cached entry in free.

Note that before proceeding to use TMPFS or RAMFS you should know besides having advantages, there are certain serious disadvantage that if the server using tmpfs (in RAM) to store files crashes the customer might loose his data, therefore using RAM filesystems on Production servers is best to be used just for caching folders which are regularly synchronized with (rsync) to some folder to assure no data will be lost on server reboot or crash.

Memory of fast storage areas are ideally suited for applications which need repetitively small data areas for caching or using as temporary space such as Jira (Issue and Proejct Tracking Software) Indexing  As the data is lost when the machine reboots the tmpfs stored data must not be data of high importance as even scheduling backups cannot guarantee that all the data will be replicated in the even of a system crash.

To test mounting a tmpfs virtual (memory stored) filesystem issue:
 

mount -t tmpfs tmpfs -o size=256m /mnt/tmpfs


If you want to test mount a ramfs instead:

 

 mount -t ramfs -o size=256m ramfs /mnt/ramfs

 

debian-server:~#  mount |grep -i -E "ramfs|tmpfs"
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
tmpfs on /mnt/tmpfs type tmpfs (rw,size=256m)
ramfs on /mnt/ramfs type tmpfs (rw,size=256m)

 

Once mounted tmpfs can be used in the same way as any ext4 / reiserfs filesystem. In the same way to make mounts permanent, its necessery to add a line to /etc/fstab

To illustrate better a tmpfs use case on my blog running WordPress with W3TotalCache (W3TC) plugin cache folder in /var/www/blog/wp-content/w3tc to get advantage of tmpfs to store w3tc files.

a) Stop Apache

On Debian
 

debian-server:~# /etc/init.d/apache stop


On CentOS 
 

[root@centos ~]# /etc/init.d/httpd stop


b) Move w3tc dir to w3tc-bak

 

debian-server:~# cd /var/www/blog/wp-content/
debian-server:~# mv w3tc w3tc-bak

 

c) Create w3tc directory
 

debian-server:/var/www/blog/wp-content# mkdir w3tc
debian-server:/var/www/blog/wp-content# chown -R www-data:www-data w3tc


d) Add tmpfs record to /etc/fstab

My W3TC Cache didn't grow bigger than 2Gigabytes so I create a 2Giga directory for it by adding following in /etc/fstab 
 

debian-server:~# vim /etc/fstab

 

tmpfs /var/www/blog/wp-content/w3tc tmpfs defaults,size=2g,noexec,nosuid,uid=33,gid=33,mode=1755 0 0


You might also want to add the nr_inodes (option) to tmpfs while mounting. nr_inodes is the maximum inode for instance. Default is half the number of your physical RAM pages, (on a machine with highmem) the number of lowmem RAM page, some common option that should work is nr_inodes=5k, if you're unsure what this option does you can safely skip it 🙂

e) Mount new added tmpfs folder

Then to mount the newly added filesystem issue:
 

mount -a


Or if you're on a CentOS / RHEL server use httpd Apache user instead and whenever you have docroot and wordpress installed.

 

[root@centos ~]# chown -R apache:apache: w3tc


If you're using Apache SuPHP use whatever the UID / GID is proper.

On CentOS you will need to set proper UID and GID (UserID / GroupID), to find out which ones to to use check in /etc/passwd:
 

[root@centos ~]# grep -i apache /etc/passwd
apache:x:48:48:Apache:/var/www:/sbin/nologin


f) Move old w3tc cache from w3tc-bak to w3tc

 

debian-server:/var/www/blog/wp-content# mv w3tc-bak/* w3tc/

 

g) Start again Apache

On Debian:

 

debian-server:~# /etc/init.d/apache2 start

 


On CentOS:
 

[root@centos~]# /etc/init.d/httpd start

h) Keeping w3tc cache site folder synced

As I said earlier the biggest problem with caching (the reason why many hosting providers) and site admins refuse to use it is they might loose some data, to prevent data loss or at least mitigate the data loss to few minutes intervals it is a good idea to synchronize tmpfs kept folders somewhere to disk with rsync.

To achieve that use a cronjob like this:
 

debian-server:~# crontab -u root -e
*/5 * * * * /usr/bin/ionice -c3 -n7 /usr/bin/nice -n 19 /usr/bin/rsync -ah –stats –delete /var/www/blog/wp-content/w3tc/ /backups/tmpfs/cache/ 1>/dev/null


Note that you will need to have the /backups/tmpfs/cache folder existing, create it with:

 

debian-server:~# mkdir -p /backups/tmpfs/cache


You will also need to add a rsync synchronization from backupped folder to tmpfs (in case if the server gets accidently rebooted because it hanged or power outage), place in

/etc/rc.local

 

ionice -c3 -n7 nice -n 19 rsync -ahv –stats –delete /backups/tmpfs/cache/ /var/www/blog/wp-content/w3tc/ 1>/dev/null


(somewhere before exit 0) line
 

0 05 * * * /usr/bin/ionice -c3 -n7 /bin/nice -n 19 /usr/bin/rsync -ah –stats –delete /var/www/blog/wp-content/w3tc/ /backups/tmpfs/cache/ 1>/dev/null

 

 

2. Preparing tmpfs partitions for MySQL server temp File Cache directory


Its common that MySQL servers had to serve a lot of long and heavy SQL JOIN Queries mostly by related posts WP plugins such as (Zemanta Related Posts) and Contextual Related posts though MySQLs are well optimized  to work as much as efficient using mysql tuner (tuning primer) still often SQL servers get a lot of temp tables created to disk (about 25% to 30%) of all SQL queries use somehow HDD to serve queries and as this is very slow and there is file lock created the overall MySQL performance becomes sluggish at times to fix (resolve) that without playing with SQL code to optimize the slow queries the best way I found is by using TMPFS as MySQL temp folder.

To do so I create a TMPFS usually the size of 256 MB because this is usually enough for us, but other hosting companies might want to add bigger virtual temp disk:

a) Add tmpfs new dir to /etc/fstab

In /etc/fstab add below record with vim editor:
 

debian-server:~# vim /etc/fstab

 

tmpfs /var/mysqltmp tmpfs rw,gid=111,uid=108,size=256M,nr_inodes=10k,mode=0700 0 0

 

Note that the uid / and gid 105 and 114 are taken again from /etc/passwd

On Debian

debian-server:~# grep -i mysql /etc/passwd
mysql:x:108:111:MySQL Server,,,:/var/lib/mysql:/bin/false


On CentOS
 

[root@centos ~]# grep -i mysql /etc/passwd
mysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/bash


b) Create folder /var/mysqltmp or whenever you want to place the tmpfs memory kept SQL folder

 

debian-server:~# mkdir /var/mysqltmp
debian-server:~# chown mysql:mysql /var/mysqltmp

 

debian-server:~# mount|grep -i tmpfs
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
tmpfs on /var/www/blog/wp-content/w3tc type tmpfs (rw,noexec,nosuid,size=2g,uid=33,gid=33,mode=1755)
tmpfs on /var/mysqltmp type tmpfs (rw,gid=108,uid=111,size=256M,nr_inodes=10k,mode=0700)


c) Add new path to tmpfs created folder in my.cnf 

Then  edit /etc/mysql/my.cnf

 

debian-server:~# vim /etc/mysql/my.cnf

[mysqld]
#
# * Basic Settings
#
user        = mysql
pid-file    = /var/run/mysqld/mysqld.pid
socket      = /var/run/mysqld/mysqld.sock
port        = 3306
basedir     = /usr
datadir     = /var/lib/mysql
tmpdir      = /var/mysqltmp

 

On CentOS edit and change tmpdir in same way within /etc/my.cnf


d) Finally Restart Apache and MySQL to make mysql start using new set tmpfs memory kept folder

On Debian:
 

debian-server:~# /etc/init.d/apache2 stop; /etc/init.d/mysql restart; /etc/init.d/apache2 start

On CentOS:
 

[root@centos ~]# /etc/init.d/httpd stop; /etc/init.d/mysqld restart; /etc/initd/httpd start


Now monitor your server and check your pagespeed increase for me such an optimization usually improves site performance so site becomes +50% faster, to see the difference you can test your website before applying tmpfs caching for site and after that by using Google PageInsight (PageSpeed) Online Test. Though this example is for MySQL and WordPress you can easily adopt the same for Joomla if you have Joomla Caching enabled to some folder, same goes for any other CMS such as Drupal that can take use of Disk Caching. Actually its a small secret of many Hosting providers that allow clients to create sites via CPanel and Kloxo this tmpfs optimizations are already used for sites and by this the provider is able to offer better website service on lower prices. VPS hosting providers also use heavy caching. A lot of people are using TMPFS also to accelerate Sites that have enabled Google Pagespeed as Cacher and accelerator, as PageSpeed module puts a heavy HDD I/O load that can easily stone the server. Many admins also choose to use TMPFS for  /tmp, /var/run, and /var/lock directories as this leads often to significant overall server services operations improvement.
Once you have tmpfs enabled, It is a good idea to periodically monitor your SWAP used space with (df -h), because if you allocate bigger tmpfs partitions than your physical memory and tmpfs's full size starts to be used your machine will start swapping heavily and this could have a very negative performance affect.
 

debian-server:~# df -h|grep -i tmpfs
tmpfs            3,9G     0   3,9G   0% /lib/init/rw
tmpfs            3,9G     0   3,9G   0% /dev/shm
tmpfs            2,0G  1,4G   712M  66% /var/www/blog/wp-content/w3tc
tmpfs            256M     0   256M   0% /mnt/tmpfs
tmpfs            256M  236K   256M   1% /var/mysqltmp

The applications of tmpfs to accelerate services is up to your imagination, so I will be glad to hear from other admins on any interesting other application or problems faced while using TMPFS.

 Enjoy! 🙂

Tags: , , , , , , , , , , , , , , , , , , , , , , , ,
Posted in Linux, MySQL, System Administration, Various, Web and CMS | 1 Comment »

How to make a mirror of website on GNU / Linux with wget / Few tips on wget site mirroring

Wednesday, February 22nd, 2012

how-to-make-mirror-of-website-on-linux-wget

Everyone who used Linux is probably familiar with wget or has used this handy download console tools at least thousand of times. Not so many Desktop GNU / Linux users like Ubuntu and Fedora Linux users had tried using wget to do something more than single files download.
Actually wget is not so popular as it used to be in earlier linux days. I've noticed the tendency for newer Linux users to prefer using curl (I don't know why).

With all said I'm sure there is plenty of Linux users curious on how a website mirror can be made through wget.
This article will briefly suggest few ways to do website mirroring on linux / bsd as wget is both available on those two free operating systems.

1. Most Simple exact mirror copy of website

The most basic use of wget's mirror capabilities is by using wget's -mirror argument:

# wget -m http://website-to-mirror.com/sub-directory/

Creating a mirror like this is not a very good practice, as the links of the mirrored pages will still link to external URLs. In other words link URL will not pointing to your local copy and therefore if you're not connected to the internet and try to browse random links of the webpage you will end up with many links which are not opening because you don't have internet connection.

2. Mirroring with rewritting links to point to localhost and in between download page delay

Making mirror with wget can put an heavy load on the remote server as it fetches the files as quick as the bandwidth allows it. On heavy servers rapid downloads with wget can significantly reduce the download server responce time. Even on a some high-loaded servers it can cause the server to hang completely.
Hence mirroring pages with wget without explicity setting delay in between each page download, could be considered by remote server as a kind of DoS – (denial of service) attack. Even some site administrators have already set firewall rules or web server modules configured like Apache mod_security which filter requests to IPs which are doing too frequent HTTP GET /POST requests to the web server.
To make wget delay with a 10 seconds download between mirrored pages use:

# wget -mk -w 10 -np --random-wait http://website-to-mirror.com/sub-directory/

The -mk stands for -m/-mirror and -k / shortcut argument for –convert-links (make links point locally), –random-wait tells wget to make random waits between o and 10 seconds between each page download request.

3. Mirror / retrieve website sub directory ignoring robots.txt "mirror restrictions"

Some websites has a robots.txt which restricts content download with clients like wget, curl or even prohibits, crawlers to download their website pages completely.

/robots.txt restrictions are not a problem as wget has an option to disable robots.txt checking when downloading.
Getting around the robots.txt restrictions with wget is possible through -e robots=off option.
For instance if you want to make a local mirror copy of the whole sub-directory with all links and do it with a delay of 10 seconds between each consequential page request without reading at all the robots.txt allow/forbid rules:

# wget -mk -w 10 -np -e robots=off --random-wait http://website-to-mirror.com/sub-directory/

4. Mirror website which is prohibiting Download managers like flashget, getright, go!zilla etc.

Sometimes when try to use wget to make a mirror copy of an entire site domain subdirectory or the root site domain, you get an error similar to:

Sorry, but the download manager you are using to view this site is not supported.
We do not support use of such download managers as flashget, go!zilla, or getright

This message is produced by the site dynamic generation language PHP / ASP / JSP etc. used, as the website code is written to check on the browser UserAgent sent.
wget's default sent UserAgent to the remote webserver is:
Wget/1.11.4

As this is not a common desktop browser useragent many webmasters configure their websites to only accept well known established desktop browser useragents sent by client browsers.
Here are few typical user agents which identify a desktop browser:
 

  • Mozilla/5.0 (Windows NT 6.1; rv:6.0) Gecko/20110814 Firefox/6.0
  • Mozilla/5.0 (X11; Linux i686; rv:6.0) Gecko/20100101 Firefox/6.0
  • Mozilla/6.0 (Macintosh; I; Intel Mac OS X 11_7_9; de-LI; rv:1.9b4) Gecko/2012010317 Firefox/10.0a4
  • Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:2.2a1pre) Gecko/20110324 Firefox/4.2a1pre

etc. etc.

If you're trying to mirror a website which has implied some kind of useragent restriction based on some "valid" useragent, wget has the -U option enabling you to fake the useragent.

If you get the Sorry but the download manager you are using to view this site is not supported , fake / change wget's UserAgent with cmd:

# wget -mk -w 10 -np -e robots=off \
--random-wait
--referer="http://www.google.com" \--user-agent="Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6" \--header="Accept:text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5" \--header="Accept-Language: en-us,en;q=0.5" \--header="Accept-Encoding: gzip,deflate" \--header="Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7" \--header="Keep-Alive: 300"

For the sake of some wget anonimity – to make wget permanently hide its user agent and pretend like a Mozilla Firefox running on MS Windows XP use .wgetrc like this in home directory.

5. Make a complete mirror of a website under a domain name

To retrieve complete working copy of a site with wget a good way is like so:

# wget -rkpNl5 -w 10 --random-wait www.website-to-mirror.com

Where the arguments meaning is:
-r – Retrieve recursively
-k – Convert the links in documents to make them suitable for local viewing
-p – Download everything (inline images, sounds and referenced stylesheets etc.)
-N – Turn on time-stamping
-l5 – Specify recursion maximum depth level of 5

6. Make a dynamic pages static site mirror, by converting CGI, ASP, PHP etc. to HTML for offline browsing

It is often websites pages are ending in a .php / .asp / .cgi … extensions. An example of what I mean is for instance the URL http://php.net/manual/en/tutorial.php. You see the url page is tutorial.php once mirrored with wget the local copy will also end up in .php and therefore will not be suitable for local browsing as .php extension is not understood how to interpret by the local browser.
Therefore to copy website with a non-html extension and make it offline browsable in HTML there is the –html-extension option e.g.:

# wget -mk -w 10 -np -e robots=off \
--random-wait \
--convert-links http://www.website-to-mirror.com

A good practice in mirror making is to set a download limit rate. Setting such rate is both good for UP and DOWN side (the local host where downloading and remote server). download-limit is also useful when mirroring websites consisting of many enormous files (documental movies, some music etc.).
To set a download limit to add –limit-rate= option. Passing by to wget –limit-rate=200K would limit download speed to 200KB.

Other useful thing to assure wget has made an accurate mirror is wget logging. To use it pass -o ./my_mirror.log to wget.
 

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,
Posted in Linux, System Administration, Web and CMS | 2 Comments »

How to enable output compression (gzipfile content compression) in nginx webserver

Friday, April 8th, 2011

I have recently installed and configured a Debian Linux server with nginx
. Since then I’ve been testing around different ways to optimize the nginx performance.

In my nginx quest, one of the most crucial settings which dramatically improved the end client performance was enabling the so called output compression which in Apache based servers is also known as content gzip compression .
In Apache webservers the content gzip compression is provided by a server module called mod_deflate .

The output compression nginx settings saves a lot of bandwidth and though it adds up a bit more load to the server, the plain text files like html, xml, js and css’s download time reduces drasticly as they’re streamed to the browser in gzip compressed format.
This little improvement in download speed also does impact the overall end user browser experience and therefore improves the browsing speed experience with websites.

If you have already had experience nginx you already know it is a bit fastidious and you have to be very careful with it’s configuration, however thanksfully enabling the gzip compression was actually rather easier than I thought.

Here is what I added in my nginx config to enable output compression:

## Compression
gzip on;
gzip_buffers 16 8k;
gzip_comp_level 9;
gzip_http_version 1.1;
gzip_min_length 0;
gzip_vary on;

Important note here is that need to add this code in the nginx configuration block starting with:

http {
....
## Compression
gzip on;
gzip_buffers 16 8k;
gzip_comp_level 9;
gzip_http_version 1.1;
gzip_min_length 0;
gzip_vary on;

In order to load the gzip output compression as a next step you need to restart the nginx server, either by it’s init script if you use one or by killing the old nginx server instances and starting up the nginx server binary again:
I personally use an init script, so restarting nginx for me is done via the cmd:

debian:~# /etc/init.d/nginx restart
Restarting nginx: nginx.

Now to test if the output gzip compression is enabled for nginx, you can simply use telnet

hipo@linux:~$ telnet your-nginx-webserver-domain.com 80
Escape character is '^]'.

After the Escape character is set ‘^]’ appears on your screen type in the blank space:

HEAD / HTTP/1.0

and press enter twice.
The output which should follow should look like:


HTTP/1.1 200 OK
Server: nginx
Date: Fri, 08 Apr 2011 12:04:43 GMT
Content-Type: text/html
Content-Length: 13
Last-Modified: Tue, 22 Mar 2011 15:04:26 GMT
Connection: close
Vary: Accept-Encoding
Expires: Fri, 15 Apr 2011 12:04:43 GMT
Cache-Control: max-age=604800
Accept-Ranges: bytes

The whole transaction with telnet command issued and the nginx webserver output should look like so:

hipo@linux:~$ telnet your-nginx-webserver-domain.com 80
Trying xxx.xxx.xxx.xxx...
Connected to your-nginx-webserver-domain.com
.Escape character is '^]'.
HEAD / HTTP/1.0

HTTP/1.1 200 OK
Server: nginx
Date: Fri, 08 Apr 2011 12:04:43 GMT
Content-Type: text/html
Content-Length: 13
Last-Modified: Tue, 22 Mar 2011 15:04:26 GMT
Connection: close
Vary: Accept-Encoding
Expires: Fri, 15 Apr 2011 12:04:43 GMT
Cache-Control: max-age=604800
Accept-Ranges: bytes

The important message in the returned output which confirms your nginx output compression is properly configured is:

Vary: Accept-Encoding

If this message is returned by your nginx server, this means your nginx now will distribute it’s content to it’s clients in compressed format and apart from the browsing boost a lot of server and client bandwitdth will be saved.

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,
Posted in Linux, System Administration, Web and CMS | 3 Comments »

How much memory users uses in GNU / Linux and FreeBSD – Commands and Scripts to find user memory usage on Linux

Tuesday, February 17th, 2015

 

how-much-memory-users-use-in-gnu-linux-freebsd-command-to-find-and-show-ascending-descending-usage-of-system-memory-tux-memory-logo

 


If you have to administrate a heterogenous network with Linux and FreeBSD or other UNIX like OSes you should sooner or later need for scripting purposes to have a way to list how much memory separate users take up on your system. Listing memory usage per user is very helpful for admins who manager free-shells or for companies where you have developers, developing software directly on the server via ssh. Being able to check which process eats up most memory is essential for every UNIX / Linux sysadmin, because often we as admins setup (daemons) on servers and we forgot about their existence, just to remember they exist 2 years later and see the server is crashing because of memory exhaustion. Tracking server bottlenecks where RAM memory and Swapping is the bottleneck is among the main swiss amry knives of admins. Checking which user occupies all server memory is among the routine tasks we're forced to do as admins, but because nowdays servers have a lot of memory and we put on servers often much more memory than ever will be used many admins forget to routinely track users / daemons memory consumption or even many probably doesn't know how.  Probably all are aware of the easiest wy to get list of all users memory in console non interactively with free command, e.g.:
 

free -m
             total       used       free     shared    buffers     cached
Mem:         32236      26226       6010          0        983       8430
-/+ buffers/cache:      16812      15424
Swap:        62959        234      62725

 

but unfortunately free command only shows overall situation with memory and doesn't divide memory usage by user

Thus probably to track memory users the only known way for most pepole is to (interactively) use good old top command or if you like modern (colorful) visualization with htop:

debian:~# top

 

linux-check_memory_usage_by_logged-in-user-with-top-process-command-gnu-linux-freebsd-screenshot

Once top runs interactive press 'm' to get ordered list of processes which occupy most system memory on Linux server.Top process use status statistics will refresh by default every '3.0' seconds to change that behavior to '1' second press  s and type '1.0'. To get Sort by Memory Use in htop also press 'm'
 

[root@mail-server ~]# htop


htop_show_users_memory_usage_order_ascending-gnu-linux-screenshot

 

However if you need to be involved in scripting and setting as a cron job tasks to be performed in case if high memroy consumption by a service you will need to use few lines of code. Below are few examples on how Linux user memory usage can be shown with ps cmd.

Probably the most universal way to see memory usage by users on Debian / Ubuntu / CentOS / RHEL and BSDs (FreeBSD / NetBSD) is with below one liner:

 

server:~# ps hax -o rss,user | awk '{a[$2]+=$1;}END{for(i in a)print i” “int(a[i]/1024+0.5);}' | sort -rnk2
daemon 0
debian-tor 63
dnscache 1
dnslog 0
hipo 21
messagebus 1
mysql 268
ntp 2
privoxy 1
proftpd 1
qmaill 0
qmailq 0
qmailr 0
qmails 0
qscand 291
root 94
shellinabox 1
snmp 1
statd 1
vpopmail 80
www-data 6765

 

Output is in MBs

Below is output from machine where this blog is running, the system runs ( Apache + PHP + MySQL Webserver + Qmail Mail server and Tor) on Debian GNU / Linux.

 To get more human readable (but obscure to type – useful for scripting) output list of which user takes how much memory use on deb / rpm etc. based Linux :

 

server:~# echo "USER                 RSS      PROCS" ; echo "——————– ——– —–" ; \
ps hax -o rss,user | awk '{rss[$2]+=$1;procs[$2]+=1;}END{for(user in rss) printf “%-20s %8.0f %5.0f\n”, user, rss[user]/1024, procs[user];}' | sort -rnk2

 

USER                 RSS      PROCS
——————– ——– —–
www-data                 6918   100
qscand                    291     2
mysql                     273     1
root                       95   120
vpopmail                   81     4
debian-tor                 63     1
hipo                       21    15
ntp                         2     1
statd                       1     1
snmp                        1     1
shellinabox                 1     2
proftpd                     1     1
privoxy                     1     1
messagebus                  1     1
dnscache                    1     1
qmails                      0     2
qmailr                      0     1
qmailq                      0     2
qmaill                      0     4
dnslog                      0     1
daemon                      0     2

 

It is possible to get the list of memory usage listed in percentage proportion, with a tiny for bash loop and some awk + process list command
 

TOTAL=$(free | awk '/Mem:/ { print $2 }')
for USER in $(ps haux | awk '{print $1}' | sort -u)
do
    ps hux -U $USER | awk -v user=$USER -v total=$TOTAL '{ sum += $6 } END { printf "%s %.2f\n", user, sum / total * 100; }'
done

107 1.34
115 2.10
119 1.34
daemon 1.32
dnscache 1.34
dnslog 1.32
hipo 1.59
mysql 4.79
ntp 1.34
privoxy 1.33
proftpd 1.32
qmaill 1.33
qmailq 1.33
qmailr 1.32
qmails 1.33
qscand 4.98
root 1.33
snmp 1.33
statd 1.33
vpopmail 2.35
www-data 86.48

Also a raw script which can be easily extended to give you some custom information on memory use by user list_memory_use_by_user.sh is here.
You can also want to debug further how much memory a certain users (lets say user mysql and my username hipo) is allocating, this can easily be achieved ps like so:
 

root@pcfreak:~# ps -o size,pid,user,command -u mysql –sort -size
 SIZE   PID USER     COMMAND
796924 14857 mysql   /usr/sbin/mysqld –basedir=/usr –datadir=/var/lib/mysql –plugin-dir=/usr/lib/mysql/plugin –user=mysql –pid-file=/var/run/mysqld/mysqld.pid –socket=/var/run/mysqld/mysqld.sock –port=3306

 

root@pcfreak~# ps -o size,pid,user,command -u hipo –sort -size|less
 SIZE   PID USER     COMMAND
13408 19063 hipo     irssi
 3168 19020 hipo     SCREEN
 2940  2490 hipo     -bash
 1844 19021 hipo     /bin/bash
 1844 19028 hipo     /bin/bash
 1844 19035 hipo     /bin/bash
 1844 19042 hipo     /bin/bash
 1844 19491 hipo     /bin/bash
 1844 22952 hipo     /bin/bash
  744  2487 hipo     sshd: hipo@pts/0
  744  2516 hipo     sshd: hipo@notty
  524  2519 hipo     screen -r
  412  2518 hipo     /usr/lib/openssh/sftp-server

You see from below output user running with www-data (this is Apache Webserver user in Debian) is eating 86.48% of overall system memory and MySQL server user is using only 4.79% of available memory

Output is shown in Megabytes per username memory usage, and user memory usage is ordered (stepping-down / descentive) from top to bottom

Getting more thoroughful and easier to read reporting without beeing a 31337 bash coder you can install and use on Linux smem – memory reporting tool .

SMEM can provide you with following memory info:

  • system overview listing
  • listings by process, mapping, user
  • filtering by process, mapping, or user
  • configurable columns from multiple data sources
  • configurable output units and percentages
  • configurable headers and totals
  • reading live data from /proc
  • reading data snapshots from directory mirrors or compressed tarballs
  • lightweight capture tool for embedded systems
  • built-in chart generation


Installing smem on Debian 6 / 7 / Ubuntu 14.04 / Turnkey Linux etc. servers is done with standard:

 

debian:~# apt-get install –yes smem
….
 

 

To install smem on CentOS 6 / 7:

 

[root@centos ~ ]# yum -y install smem
….


On Slackware and other Linux-es where smem is not available as a package you can install it easily from binary archive with:

 

cd /tmp/
wget http://www.selenic.com/smem/download/smem-1.3.tar.gz
tar xvf smem-1.3.tar.gz
sudo cp /tmp/smem-1.3/smem /usr/local/bin/
sudo chmod +x /usr/local/bin/smem

 


Two most common smem uses are:

 

root@mail:~# smem -u
User     Count     Swap      USS      PSS      RSS
dnslog       1       44       48       54      148
qmaill       4      232      124      145      464
hipo        11    13552     8596     9171    13160
qscand       2     4500   295336   295602   297508
root       188   217312  4521080  4568699  7712776

 

Below command shows (-u – Report memory usage by user, -t – show totals, -k – show unix suffixes)

root@mail:~# smem -u -t -k
User     Count     Swap      USS      PSS      RSS
dnslog       1    44.0K    48.0K    54.0K   148.0K
qmaill       4   232.0K   124.0K   145.0K   464.0K
hipo        11    13.2M     8.4M     9.0M    12.9M
qscand       2     4.4M   288.4M   288.7M   290.5M
root       188   212.2M     4.3G     4.4G     7.4G
—————————————————
           206   230.1M     4.6G     4.6G     7.7G


To get users memory use by percentage with smem:
 

root@mail:~# smem -u -p
User     Count     Swap      USS      PSS      RSS
dnslog       1    0.00%    0.00%    0.00%    0.00%
qmaill       4    0.00%    0.00%    0.00%    0.01%
hipo        11    0.17%    0.11%    0.11%    0.16%
qscand       2    0.05%    3.63%    3.63%    3.66%
root       194    2.64%   56.18%   56.77%   95.56%

It is also useful sometimes when you want to debug system overloads caused by external hardware drivers loaded into kernel causing issues to get list of system wide memory use sorted by user

 

 root@mail:~# smem -w -p
Area                           Used      Cache   Noncache
firmware/hardware             0.00%      0.00%      0.00%
kernel image                  0.00%      0.00%      0.00%
kernel dynamic memory        38.30%     36.01%      2.28%
userspace memory             60.50%      0.98%     59.53%
free memory                   1.20%      1.20%      0.00%


smem is very nice as if you're running it on a Desktop Linux system with Xserver installed you can see also graphical output of memory use by application:
 

root@desktop-pc:~# smem –bar pid -c "pss uss"


smem_graphical_representation-of-which-user-application-is-consuming-most-memory-gnu-linux-kde-screenshot-smem-command-line-tool

smem can even generate graphical pie charts to visualize better memory use
 

root@desktop-pc:~# smem -P '^k' –pie=name

 

generate-graphical-staticstics-linux-memory-use-by-pie-chart

If there is a high percentage shown in firmware/hardware this means some buggy module is loaded in kernel eating up memory, to fix it debug further and remove the problematic module.
userspace memory actually shows the percantage of memory out of all server available RAM that is being consumed by applications (non kernel and other system processes which make the system move). You see in above example the kernel itself is consuming about 40% of system overall available memory. 

We all know the SWAP field stands for hard disk drive used as a memory when system is out, but there are 3 fields which smem will report which will be probably unclear for most here is also explanation on what USS / PSS / RSS means?

RSS is the Resident Set Size and is used to show how much memory is allocated to that process and is in RAM. It does not include memory that is swapped out. It does include memory from shared libraries as long as the pages from those libraries are actually in memory. It does include all stack and heap memory too.

There is also PSS (proportional set size). This is a newer measure which tracks the shared memory as a proportion used by the current process. So if there were two processes using the same shared library from before.

USS stands for Unique set size, USS is just the unshared page count, i.e. memory returned when process is killed 

PSS = Proportional set size, (PSS),  is a more meaningful representation of the amount of memory used by libraries and applications in a virtual memory system.  
Because large portions of physical memory are typically shared among multiple applications, the standard measure of memory usage known as resident set size (RSS) will significantly overestimate memory usage. The parameter PSS instead measures each application’s “fair share” of each shared area to give a realistic measure. For most admins checking out the output from RSS (output) should be enough, it will indicate which user and therefore which daemon is eating up all your memory and will help you to catch problematic services which are cause your server to run out of RAM and start swapping to disk.

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , ,
Posted in Curious Facts, Linux, Linux and FreeBSD Desktop, Linux Audio & Video, System Administration | No Comments »

« Older Entries
Newer Entries »