Posts Tagged ‘cron’

Linux: how to show all users crontab – List all cronjobs

Thursday, May 22nd, 2014

linux-unix-list-all-crontab-users-and-scripts
I'm doing another server services decomissioning and part of decomissioning plan is: Removing application and all related scripts from related machines (FTP, RSYNC, …). In project documentation I found a list with Cron enabled shell scripts:

#Cron tab excerpt:
1,11,21,31,41,51 * * * */webservices/tools/scripts/rsync_portal_sync.sh

that has to be deleted, however there was nowhere mentioned under what kind of credentials (with what kind of user) are the cron scripts running? Hence I had to look up all users that has cronjobs and find inside each user's cronjobs whether respective script is set to run. Herein I will explain shortly how I did that.

Cronjobs by default has few locations from where cronjobs are setupped depending on their run time schedule. First place I checked for the scripts is

/etc/crontabs # cat /etc/crontabs SHELL=/bin/sh
PATH=/usr/bin:/usr/sbin:/sbin:/bin:/usr/lib/news/bin
MAILTO=root
#
# check scripts in cron.hourly, cron.daily, cron.weekly, and cron.monthly
#
-*/15 * * * * root test -x /usr/lib/cron/run-crons && /usr/lib/cron/run-crons >/dev/null 2>&1
59 * * * * root rm -f /var/spool/cron/lastrun/cron.hourly
14 4 * * * root rm -f /var/spool/cron/lastrun/cron.daily
29 4 * * 6 root rm -f /var/spool/cron/lastrun/cron.weekly
44 4 1 * * root rm -f /var/spool/cron/lastrun/cron.monthly

I was not really user via what user is shell script run, therefore I looked first if someone doesn't set the script to run via crontab's standard locations for Daily, Hourly,Weekly and Monthly cronjobs:
 

a) Daily set cron jobs are in:

/etc/cron.daily/

b) Hourly set cron jobs:

/etc/cron.hourly

c) Weekly cron jobs are in:

/etc/cron.weekly/

d) Monthly cron jobs:

/etc/cron.monthly

There is also a location read by crontab for all Software (package distribution) specific cronjobs – all run under root user privileges.:

e) Software specific script cron jobs are in:

/etc/cron.d/  
As the system has about 327 users in /etc/passwd, checking each user's cronjob manually with:

# crontab -u UserName -l

was too much time consuming thus it is a good practice to list

/var/spool/cron/*

directory and to see which users has cron jobs defined

 

# ls -al /var/spool/cron/*
-rw——- 1 root root 11 2007-07-09 17:08 /var/spool/cron/deny

/var/spool/cron/lastrun:
total 0
drwxr-xr-x 2 root root 80 2014-05-22 11:15 .
drwx—— 4 root root 120 2008-02-25 15:45 ..
-rw-r–r– 1 root root 0 2014-05-22 04:15 cron.daily

/var/spool/cron/tabs:
total 8
drwx—— 2 root root 72 2014-04-03 03:43 .
drwx—— 4 root root 120 2008-02-25 15:45 ..
-rw——- 1 root root 4901 2014-04-03 03:43 root
 


/var/spool/cron – is crond (/usr/bin/cron/)'s spool directory.

# ls -al /var/spool/cron/tabs/ total 8
drwx------ 2 root root 72 2014-04-03 03:43 .
drwx------ 4 root root 120 2008-02-25 15:45 ..
-rw------- 1 root root 4901 2014-04-03 03:43 root

Above output shows only root superuser has defined crons.

Alternative way to check all user crontabs is via quick Linux one liner shell script show all user cron jobs

for i in $(cat /etc/passwd | sed -e "s#:# #g" | awk '{ print $1 }'); do
echo "user $i --- crontab ---";
crontab -u $i -l 2>&1 >/dev/null;
echo '----------';
done|less

Note that above short script has to run with root user. Enjoy 🙂

Linux: List last 10 (newest) and 10 oldest modified files in a directory with ls

Tuesday, April 8th, 2014

An useful thing on GNU / Linux sometimes is to list last or oldest modified files in directory.

Lets say you want to list last 10 modified files with ls from today / yesterday. Here is how:
 

ls -1t | head -10
my.cnf
wordperss_enabled_plugins.txt
newcerts/
mysql-hipo_pcfreakbiz.dump
NewArchive-Jan-10-15.zip
hipo_pcfreakbiz-mysqldb-any-out-1389361234.tgz
Tisho_Snimki/
wordpress/
wp-cron.php?doing_wp_cron=1.1
wp-cron.php

 

To list 10 oldest modified files on Linux:

 

ls -1t | tail -10
    my.cnf
    pcfreak_sql-15_10_05_2012
    mysql-tuning-primer*
    tuning-primer.sh*
    system-administration-services.html
    blog_backup_15_07_2012.tar.gz
    www-files/
    dump.sql
    courier-imap*
    djbdns-1.05.tar.gz


Cheers 😉

How to count lines of PHP source code in a directory (recursively)

Saturday, July 14th, 2012

Count PHP and other programming languages lines of source code (source code files count) recursively

Being able to count the number of PHP source code lines for a website is a major statistical information for timely auditting of projects and evaluating real Project Managment costs. It is inevitable process for any software project evaluation to count the number of source lines programmers has written.
In many small and middle sized software and website development companies, it is the system administrator task to provide information or script quickly something to give info on the exact total number of source lines for projects.

Even for personal use out of curiousity it is useful to know how many lines of PHP source code a wordpress or Joomla website (with the plugins) contains.
Anyone willing to count the number of PHP source code lines under one directory level, could do it with:::

serbver:~# cd /var/www/wordpress-website
server:/var/www/wordpress-website:# wc -l *.php
17 index.php
101 wp-activate.php
1612 wp-app.php
12 wp-atom.php
19 wp-blog-header.php
105 wp-comments-post.php
12 wp-commentsrss2.php
90 wp-config-sample.php
85 wp-config.php
104 wp-cron.php
12 wp-feed.php
58 wp-links-opml.php
59 wp-load.php
694 wp-login.php
236 wp-mail.php
17 wp-pass.php
12 wp-rdf.php
15 wp-register.php
12 wp-rss.php
12 wp-rss2.php
326 wp-settings.php
451 wp-signup.php
110 wp-trackback.php
109 xmlrpc.php
4280 total

This will count and show statistics, for each and every PHP source file within wordpress-website (non-recursively), to get only information about the total number of PHP source code lines within the directory, one could grep it, e.g.:::

server:/var/www/wordpress-website:# wc -l *.php |grep -i '\stotal$'
4280 total

The command grep -i '\stotal$' has \s in beginning and $ at the end of total keyword in order to omit erroneously matching PHP source code file names which contain total in file name; for example total.php …. total_blabla.php …. blabla_total_bla.php etc. etc.

The \s grep regular expression meaning is "put empty space", "$" is placed at the end of tital to indicate to regexp grep only for words ending in string total.

So far, so good … Now it is most common that instead of counting the PHP source code lines for a first directory level to count complete number of PHP, C, Python whatever source code lines recursively – i. e. (a source code of website or projects kept in multiple sub-directories). To count recursively lines of programming code for any existing filesystem directory use find in conjunction with xargs:::

server:/var/www/wp-website1# find . -name '*.php' | xargs wc -l
1079 ./wp-admin/includes/file.php
2105 ./wp-admin/includes/media.php
103 ./wp-admin/includes/list-table.php
1054 ./wp-admin/includes/class-wp-posts-list-table.php
105 ./wp-admin/index.php
109 ./wp-admin/network/user-new.php
100 ./wp-admin/link-manager.php
410 ./wp-admin/widgets.php
108 ./wp-content/plugins/akismet/widget.php
104 ./wp-content/plugins/google-analytics-for-wordpress/wp-gdata/wp-gdata.php
104 ./wp-content/plugins/cyr2lat-slugs/cyr2lat-slugs.php
,,,,
652239 total

As you see the cmd counts and displays the number of source code lines encountered in each and every file, for big directory structures the screen gets floated and passing | less is nice, e.g.:

find . -name '*.php' | xargs wc -l | less

Displaying lines of code for each file within the directories is sometimes unnecessery, whether just a total number of programming source code line is required, hence for scripting purposes it is useful to only get the source lines total num:::

server:/var/www/wp-website1# find . -name '*.php' | xargs wc -l | grep -i '\stotal$'

Another shorter and less CPU intensive one-liner to calculate the lines of codes is:::

server:/var/www/wp-website1# ( find ./ -name '*.php' -print0 | xargs -0 cat ) | wc -l

Here is one other shell script which displays all file names within a directory with the respective calculated lines of code

For more professional and bigger projects using pure Linux bash and command line scripting might not be the best approach. For counting huge number of programming source code and displaying various statistics concerning it, there are two other tools – SLOCCount
as well as clock (count lines of code)

Both tools, are written in Perl, so for IT managers concerned for speed of calculating projects source (if too frequent source audit is necessery) this tools might be a bit sluggish. However for most projects they should be of a great add on value, actually SLOCCount was already used for calculating the development costs of GNU / Linux and other projects of high importance for Free Software community and therefore it is proven it works well with ENORMOUS software source line code calculations written in programming languages of heterogenous origin.

sloccount and cloc packages are available in default Debian and Ubuntu Linux repositories, so if you're a Debilian user like me you're in luck:::

server:~# apt-cache search cloc$
cloc - statistics utility to count lines of code
server:~# apt-cache search sloccount$
sloccount - programs for counting physical source lines of code (SLOC)

Well that's all folks, Cheers en happy counting 😉

How to quickly check unread Gmail emails on GNU / Linux – one liner script

Monday, April 2nd, 2012

I've hit an interesting article explaining how to check unread gmail email messages in Linux terminal. The original article is here

Being able to read your latest gmail emails in terminal/console is great thing, especially for console geeks like me.
Here is the one liner script:

curl -u GMAIL-USERNAME@gmail.com:SECRET-PASSWORD \
--silent "https://mail.google.com/mail/feed/atom" | tr -d '\n' \
| awk -F '' '{for (i=2; i<=NF; i++) {print $i}}' \
| sed -n "s/

Linux Users Group M. – [7] discussions, [10] comments and [2] jobs on LinkedIn
Twitter – Lynn Serafinn (@LynnSerafinn) has sent you a direct message on Twitter!
Facebook – Sys, you have notifications pending
Twitter – Email Marketing (@optinlists) is now following you on Twitter!
Twitter – Lynn Serafinn (@LynnSerafinn) is now following you on Twitter!
NutshellMail – 32 New Messages for Sat 3/31 12:00 PM
Linux Users Group M. – [10] discussions, [5] comments and [8] jobs on LinkedIn
eBay – Deals up to 60% OFF + A Sweepstakes!
LinkedIn Today – Top news today: The Magic of Doing One Thing at a Time
NutshellMail – 29 New Messages for Fri 3/30 12:00 PM
Linux Users Group M. – [16] discussions, [8] comments and [8] jobs on LinkedIn
Ervan Faizal Rizki . – Join my network on LinkedIn
Twitter – LEXO (@LEXOmx) retweeted one of your Tweets!
NutshellMail – 24 New Messages for Thu 3/29 12:00 PM
Facebook – Your Weekly Facebook Page Update
Linux Users Group M. – [11] discussions, [9] comments and [16] jobs on LinkedIn

As you see this one liner uses curl to fetch the information from mail.google.com's atom feed and then uses awk and sed to parse the returned content and make it suitable for display.

If you want to use the script every now and then on a Linux server or your Linux desktop you can download the above code in a script file -quick_gmail_new_mail_check.sh here

Here is a screenshot of script's returned output:

Quick Gmail New Mail Check bash script screenshot

A good use of a modified version of the script is in conjunction with a 15 minutes cron job to launch for new gmail mails and launch your favourite desktop mail client.
This method is useful if you don't want a constant hanging Thunderbird or Evolution, pop3 / imap client on your system to just take up memory or dangle down the window list.
I've done a little modification to the script to simply, launch a predefined email reader program, if gmail atom feed returns new unread mails are available, check or download my check_gmail_unread_mail.sh here
Bear in mind, on occasions of errors with incorrect username or password, the script will not return any errors. The script is missing a properer error handling.Therefore, before you use the script make sure:

gmail_username='YOUR-USERNAME';
gmail_password='YOUR-PASSWORD';

are 100% correct.

To launch the script on 15 minutes cronjob, put it somewhere and place a cron in (non-root) user:

# crontab -u root -e
...
*/15 * * * * /path/to/check_gmail_unread_mail.sh

Once you read your new emails in lets say Thunderbird, close it and on the next delivered unread gmail mails, your mail client will pop up by itself again. Once the mail client is closed the script execution will be terminated.
Consised that if you get too frequently gmail emails, using the script might be annoying as every 15 minutes your mail client will be re-opened.

If you use any of the shell scripts, make sure there are well secured (make it owned only by you). The gmail username and pass are in plain text, so someone can steal your password, very easily. For a one user Linux desktops systems as my case, security is not such a big concern, putting my user only readable script permissions (e.g. chmod 0700)is enough.

Auto restart Apache on High server load (bash shell script) – Fixing Apache server temporal overload issues

Saturday, March 24th, 2012

auto-restart-apache-on-high-load-bash-shell-script-fixing-apache-temporal-overload-issues

I've written a tiny script to check and restart, Apache if the server encounters, extremely high load avarage like for instance more than (>25). Below is an example of a server reaching a very high load avarage:;

server~:# uptime
13:46:59 up 2 days, 18:54, 1 user, load average: 58.09, 59.08, 60.05
load average: 0.09, 0.08, 0.08

Sometimes high load avarage is not a problem, as the server might have a very powerful hardware. A high load numbers is not always an indicator for a serious problems. Some 16 CPU dual core (2.18 Ghz) machine with 16GB of ram could probably work normally with a high load avarage like in the example. Anyhow as most servers are not so powerful having such a high load avarage, makes the machine hardly do its job routine.

In my specific, case one of our Debian Linux servers is periodically reaching to a very high load level numbers. When this happens the Apache webserver is often incapable to serve its incoming requests and starts lagging for clients. The only work-around is to stop the Apache server for a couple of seconds (10 or 20 seconds) and then start it again once the load avarage has dropped to less than "3".

If this temporary fix is not applied on time, the server load gets increased exponentially until all the server services (ssh, ftp … whatever) stop responding normally to requests and the server completely hangs …

Often this server overloads, are occuring at night time so I'm not logged in on the server and one such unexpected overload makes the server unreachable for hours.
To get around the sudden high periodic load avarage server increase, I've written a tiny bash script to monitor, the server load avarage and initiate an Apache server stop and start with a few seconds delay in between.

#!/bin/sh
# script to check server for extremely high load and restart Apache if the condition is matched
check=`cat /proc/loadavg | sed 's/\./ /' | awk '{print $1}'`
# define max load avarage when script is triggered
max_load='25'
# log file
high_load_log='/var/log/apache_high_load_restart.log';
# location of inidex.php to overwrite with temporary message
index_php_loc='/home/site/www/index.php';
# location to Apache init script
apache_init='/etc/init.d/apache2';
#
site_maintenance_msg="Site Maintenance in progress - We will be back online in a minute";
if [ $check -gt "$max_load" ]; then>
#25 is load average on 5 minutes
cp -rpf $index_php_loc $index_php_loc.bak_ap
echo "$site_maintenance_msg" > $index_php_loc
sleep 15;
if [ $check -gt "$max_load" ]; then
$apache_init stop
sleep 5;
$apache_init restart
echo "$(date) : Apache Restart due to excessive load | $check |" >> $high_load_log;
cp -rpf $index_php_loc.bak_ap $index_php_loc
fi
fi

The idea of the script is partially based on a forum thread – Auto Restart Apache on High Loadhttp://www.webhostingtalk.com/showthread.php?t=971304Here is a link to my restart_apache_on_high_load.sh script

The script is written in a way that it makes two "if" condition check ups, to assure 100% there is a constant high load avarage and not just a temporal 5 seconds load avarage jump. Once the first if is matched, the script first tries to reduce the server load by overwritting a the index.php, index.html script of the website with a one stating the server is ongoing a maintenance operations.
Temporary stopping the index page, often reduces the load in 10 seconds of time, so the second if case is not necessery at all. Sometimes, however this first "if" condition cannot decrease enough the load and the server load continues to stay too high, then the script second if comes to play and makes apache to be completely stopped via Apache init script do 2 secs delay and launch the apache server again.

The script also logs about, the load avarage encountered, while the server was overloaded and Apache webserver was restarted, so later I can check what time the server overload occured.
To make the script periodically run, I've scheduled the script to launch every 5 minutes as a cron job with the following cron:

# restart Apache if load is higher than 25
*/5 * * * * /usr/sbin/restart_apache_on_high_load.sh >/dev/null 2>&1

I have also another system which is running FreeBSD 7_2, which is having the same overload server problems as with the Linux host.
Copying the auto restart apache on high load script on FreeBSD didn't work out of the box. So I rewrote a little chunk of the script to make it running on the FreeBSD host. Hence, if you would like to auto restart Apache or any other service on FreeBSD server get /usr/sbin/restart_apache_on_high_load_freebsd.sh my script and set it on cron on your BSD.

This script is just a temporary work around, however as its obvious that the frequency of the high overload will be rising with time and we will need to buy new server hardware to solve permanently the issues, anyways, until this happens the script does a great job 🙂

I'm aware there is also alternative way to auto restart Apache webserver on high server loads through using monit utility for monitoring services on a Unix system. However as I didn't wanted to bother to run extra services in the background I decided to rather use the up presented script.

Interesting info to know is Apache module mod_overload exists – which can be used for checking load average. Using this module once load avarage is over a certain number apache can stop in its preforked processes current serving request, I've never tested it myself so I don't know how usable it is. As of time of writting it is in early stage version 0.2.2
If someone, have tried it and is happy with it on a busy hosting servers, please share with me if it is stable enough?

Check and Restart Apache if it is malfunctioning (not returning HTML content) shell script

Monday, March 19th, 2012

Check and Restart Apache Webserver on Malfunction, Apache feather logo

One of the company Debian Lenny 5.0 Webservers, where I'm working as sys admin sometimes stops to properly server HTTP requests.
Whenever this oddity happens, the Apache server seems to be running okay but it is not failing to return requested content

I can see the webserver listens on port 80 and establishing connections to remote hosts – the apache processes show normally as I can see in netstat …:

apache:~# netstat -enp 80
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State User Inode PID/Program name
tcp 0 0 xxx.xxx.xxx.xx:80 46.253.9.36:5665 SYN_RECV 0 0 -
tcp 0 0 xxx.xxx.xxx.xx:80 78.157.26.24:5933 SYN_RECV 0 0 -
...

Also the apache forked child processes show normally in process list:

apache:~# ps axuwwf|grep -i apache
root 46748 0.0 0.0 112300 872 pts/1 S+ 18:07 0:00 \_ grep -i apache
root 42530 0.0 0.1 217392 6636 ? Ss Mar14 0:39 /usr/sbin/apache2 -k start
www-data 42535 0.0 0.0 147876 1488 ? S Mar14 0:01 \_ /usr/sbin/apache2 -k start
root 28747 0.0 0.1 218180 4792 ? Sl Mar14 0:00 \_ /usr/sbin/apache2 -k start
www-data 31787 0.0 0.1 219156 5832 ? S Mar14 0:00 | \_ /usr/sbin/apache2 -k start

In spite of that, in any client browser to any of the Apache (Virtual hosts) websites, there is no HTML content returned…
This weird problem continues until the Apache webserver is retarted.
Once webserver is restarted everything is back to normal.
I use Apache Check Apache shell script set on few remote hosts to regularly check with nmap if port 80 (www) of my server is open and responding, anyways this script just checks if the open and reachable and thus using it was unable to detect Apache wasn't able to return back HTML content.
To work around the malfunctions I wrote tiny script – retart_apache_if_empty_content_is_returned.sh

The scripts idea is very simple;
A request is made a remote defined host with lynx text browser, then the output of lines is counted, if the output returned by lynx -dump http://someurl.com is less than the number returned whether normally invoked, then the script triggers an apache init script restart.

I've set the script to periodically run in a cron job, every 5 minutes each hour.
# check if apache returns empty content with lynx and if yes restart and log it
*/5 * * * * /usr/sbin/restart_apache_if_empty_content.sh >/dev/null 2>&1

This is not perfect as sometimes still, there will be few minutes downtime, but at least the downside will not be few hours until I am informed ssh to the server and restart Apache manually

A quick way to download and set from cron execution my script every 5 minutes use:

apache:~# cd /usr/sbin
apache:/usr/sbin# wget -q http://www.pc-freak.net/bscscr/restart_apache_if_empty_content.sh
apache:/usr/sbin# chmod +x restart_apache_if_empty_content.sh
apache:/usr/sbin# crontab -l > /tmp/file; echo '*/5 * * * *' /usr/sbin/restart_apache_if_empty_content.sh 2>&1 >/dev/null

 

How to resolve (fix) WordPress wp-cron.php errors like “POST /wp-cron.php?doing_wp_cron HTTP/1.0″ 404” / What is wp-cron.php and what it does

Monday, March 12th, 2012

fix wordpress wp-cron.php 404 HTTP error, what is wp-cron.php schedule logo

One of the WordPress websites hosted on our dedicated server produces all the time a wp-cron.php 404 error messages like:

xxx.xxx.xxx.xxx - - [15/Apr/2010:06:32:12 -0600] "POST /wp-cron.php?doing_wp_cron HTTP/1.0

I did not know until recently, whatwp-cron.php does, so I checked in google and red a bit. Many of the places, I've red are aa bit unclear and doesn't give good exlanation on what exactly wp-cron.php does. I wrote this post in hope it will shed some more light on wp-config.php and how this major 404 issue is solved..
So

what is wp-cron.php doing?

 

  • wp-cron.php is acting like a cron scheduler for WordPress.
  • wp-cron.php is a wp file that controls routine actions for particular WordPress install.
  • Updates the data in SQL database on every, request, every day or every hour etc. – (depending on how it's set up.).
  • wp-cron.php executes automatically by default after EVERY PAGE LOAD!
  • Checks all pending comments for spam with Akismet (if akismet or anti-spam plugin alike is installed)
  • Sends all scheduled emails (e.g. sent a commentor email when someone comments on his comment functionality, sent newsletter subscribed persons emails etc.)
  • Post online scheduled articles for a day and time of particular day

Suppose you're writting a new post and you want to take advantage of WordPress functionality to schedule a post to appear Online at specific time:

What is wordpress wp-cron.php, Scheduling wordpress post screenshot

The Publish Immediately, field execution is being issued on the scheduled time thanks to the wp-cron.php periodic invocation.

Another example for wp-cron.php operation is in handling flushing of WP old HTML Caches generated by some wordpress caching plugin like W3 Total Cache
wp-cron.php takes care for dozens of other stuff silently in the background. That's why many wordpress plugins are depending heavily on wp-cron.php proper periodic execution. Therefore if something is wrong with wp-config.php, this makes wordpress based blog or website partially working or not working at all.
 

Our company wp-cron.php errors case

In our case the:
212.235.185.131 – – [15/Apr/2010:06:32:12 -0600] "POST /wp-cron.php?doing_wp_cron HTTP/1.0" 404
is occuring in Apache access.log (after each unique vistor request to wordpress!.), this is cause wp-cron.php is invoked on each new site visitor site request.
This puts a "vain load" on the Apache Server, attempting constatly to invoke the script … always returning not found 404 err.

As a consequence, the WP website experiences "weird" problems all the time. An illustration of a problem caused by the impoper wp-cron.php execution is when we are adding new plugins to WP.

Lets say a new wordpress extension is download, installed and enabled in order to add new useful functioanlity to the site.

Most of the time this new plugin would be malfunctioning if for example it is prepared to add some kind of new html form or change something on some or all the wordpress HTML generated pages.
This troubles are result of wp-config.php's inability to update settings in wp SQL database, after each new user request to our site.
So the newly added plugin website functionality is not showing up at all, until WP cache directory is manually deleted with rm -rf /var/www/blog/wp-content/cache/

I don't know how thi whole wp-config.php mess occured, however my guess is whoever installed this wordpress has messed something in the install procedure.

Anyways, as I researched thoroughfully, I red many people complaining of having experienced same wp-config.php 404 errs. As I red, most of the people troubles were caused by their shared hosting prohibiting the wp-cron.php execution.
It appears many shared hostings providers choose, to disable the wordpress default wp-cron.php execution. The reason is probably the script puts heavy load on shared hosting servers and makes troubles with server overloads.

Anyhow, since our company server is adedicated server I can tell for sure in our case wordpress had no restrictions for how and when wp-cron.php is invoked.
I've seen also some posts online claiming, the wp-cron.php issues are caused of improper localhost records in /etc/hosts, after a thorough examination I did not found any hosts problems:

hipo@debian:~$ grep -i 127.0.0.1 /etc/hosts
127.0.0.1 localhost.localdomain localhost

You see from below paste, our server, /etc/hosts has perfectly correct 127.0.0.1 records.

Changing default way wp-cron.php is executed

As I've learned it is generally a good idea for WordPress based websites which contain tens of thousands of visitors, to alter the default way wp-cron.php is handled. Doing so will achieve some efficiency and improve server hardware utilization.
Invoking the script, after each visitor request can put a heavy "useless" burden on the server CPU. In most wordpress based websites, the script did not need to make frequent changes in the DB, as new comments in posts did not happen often. In most wordpress installs out there, big changes in the wordpress are not common.

Therefore, a good frequency to exec wp-cron.php, for wordpress blogs getting only a couple of user comments per hour is, half an hour cron routine.

To disable automatic invocation of wp-cron.php, after each visitor request open /var/www/blog/wp-config.php and nearby the line 30 or 40, put:

define('DISABLE_WP_CRON', true);

An important note to make here is that it makes sense the position in wp-config.php, where define('DISABLE_WP_CRON', true); is placed. If for instance you put it at the end of file or near the end of the file, this setting will not take affect.
With that said be sure to put the variable define, somewhere along the file initial defines or it will not work.

Next, with Apache non-root privileged user lets say www-data, httpd, www depending on the Linux distribution or BSD Unix type add a php CLI line to invoke wp-cron.php every half an hour:

linux:~# crontab -u www-data -e

0,30 * * * * cd /var/www/blog; /usr/bin/php /var/www/blog/wp-cron.php 2>&1 >/dev/null

To assure, the php CLI (Command Language Interface) interpreter is capable of properly interpreting the wp-cron.php, check wp-cron.php for syntax errors with cmd:

linux:~# php -l /var/www/blog/wp-cron.php
No syntax errors detected in /var/www/blog/wp-cron.php

That's all, 404 wp-cron.php error messages will not appear anymore in access.log! 🙂

Just for those who can find the root of the /wp-cron.php?doing_wp_cron HTTP/1.0" 404 and fix the issue in some other way (I'll be glad to know how?), there is also another external way to invoke wp-cron.php with a request directly to the webserver with short cron invocation via wget or lynx text browser.

– Here is how to call wp-cron.php every half an hour with lynxPut inside any non-privileged user, something like:
01,30 * * * * /usr/bin/lynx -dump "http://www.your-domain-url.com/wp-cron.php?doing_wp_cron" 2>&1 >/dev/null

– Call wp-cron.php every 30 mins with wget:

01,30 * * * * /usr/bin/wget -q "http://www.your-domain-url.com/wp-cron.php?doing_wp_cron"

Invoke the wp-cron.php less frequently, saves the server from processing the wp-cron.php thousands of useless times.

Altering the way wp-cron.php works should be seen immediately as the reduced server load should drop a bit.
Consider you might need to play with the script exec frequency until you get, best fit cron timing. For my company case there are only up to 3 new article posted a week, hence too high frequence of wp-cron.php invocations is useless.

With blog where new posts occur once a day a script schedule frequency of 6 up to 12 hours should be ok.

 

Use rsync to copy from files from destination host to source host (rsync reverse copy) / few words on rsync

Monday, January 9th, 2012

I've recently had to set up a backup system to synchronize backup archive files between two remote servers and as I do usually with this situation I just set up a crontab job to periodically execute rsync to copy data from source server to the destination server . Copying SRC to DEST is the default behaviour rsync uses, however in this case I had to copy from the destination server to the source server host (in other words sync files the reversely.

The usual way to copy with rsync via SSH (from SRC to DEST) is using a cmd line like:

debian:~$ /usr/bin/rsync -avz -e ssh backup-user@xxx.xxx.xxx.xxx:/home/backup-user/my-directory .

Where the xxx.xxx.xxx.xxx is my remote server IP with which files are synched.
According to rsync manual, the proposed docs SYNOPSIS is in the format;
Local: rsync [OPTION…] SRC… [DEST

Obviusly the default way to use rsync is to copy source to destination which I used until now, but in this case I had to the other way around and copy files from a destination host to the source server. It was logical that swapping the SRC and DEST would complete my required task. Anyways I consulted with some rsync gurus in irc.freenode.net , just to make sure it is proper to just swap the SRC, DEST arguments.
I was told this is possible, so I swapped args;

debian:~$ /usr/bin/rsync -avz -e ssh . backup-user@xxx.xxx.xxx.xxx:/home/backup-user/my-directory
...

Surprisingly this worked 😉 Anyways I was adviced by by a good guy nick named scheel , that putting -e ssh to command line is generally unnecessery except if there is no some uncommon used SSH port over which the data is transferred. An example case in which -e 'ssh is necessery would be if transferring via lets say SSH port 1234;

rsync -avz -e 'ssh -p1234' /source user@host:/dest

In all other cases omitting '-e ssh' is better as '-e ssh' is rsync default. Therefore my final swapped line I put in cron to copy from a destinatio to source host with rsync looked like so:

05 03 2 * * /usr/bin/ionice -c 3 /usr/bin/rsync -avz my-directory backup-user@xxx.xxx.xxx.xxx:/home/backup-user/ >/dev/null 2>&1
 

Easy way to look for irregularities and problems in log files / Facilitate reading log files on GNU / Linux and FreeBSD

Thursday, November 24th, 2011

LogWatch logo picture check Logcheck Linux BSD look for irregularities in log files

As a System Administrator I need to check daily the log files produced on various GNU / Linux distributions or FreeBSD. This can sometimes take too much time if the old fashioned way using the normal system tools cat, less and tail etc. is used.

Reading logs one by one eats too much of my time and often as logs are reviewed in a hurry some crucial system irregularities, failed ssh or POP3 / Imap logins, filling disk spaces etc. are missed.

Therefore I decided to implement automated log parsing programs which will summary and give me an overview (helicopter view) on what were the system activities from the previous day (24h) until the moment I logged the system and issued the log analyzer program.
There are plenty of programs available out there that does “wide scale” log analysis, however there are two applications which on most GNU / Linux and BSD systems had become a de-facto standard programs to scan system log files for interesting lines.

These are:
 

  • 1. logwatchsystem log analyzer and reporter
  • 2. logcheckprogram to scan system log files for interesting lines

1. logwatch is by default installed on most of the Redhat based Linux systems (Fedora, RHEL, CentOS etc.). On Debian distributions and as far as I know (Ubuntu) and the other deb based distros logwatch is not installed by default. Most of the servers I manage these days are running Debian GNU / Linux so, to use logwatch I needed to install it from the available repository package, e.g.:

debian:~# apt-get install logwatch
...

logwatch is written in perl and with some big files to analyze, parsing them might take hell a lot of time. It does use a bunch of configuration scripts which defines how logwatch should read and parse the various services logwatch support by default. These conf scripts are also easily extensible, so if one has to analyze some undefined service in the conf files he can easily come up with a new conf script that will support the service/daemon of choice.Using logwatch is very easy, to get an overview about server system activity invoke the logwatch command:

debian:~# logwatch
################### Logwatch 7.3.6+cvs20080702-debian (07/02/08) ####################
Processing Initiated: Thu Nov 24 05:22:07 2011
Date Range Processed: yesterday
( 2011-Nov-23 )
Period is day.
Detail Level of Output: 0
Type of Output/Format: stdout / text
Logfiles for Host: debian
 ################################################# 

——————— dpkg status changes Begin ————- 

Upgraded:
libfreetype6 2.3.7-2+lenny7 => 2.3.7-2+lenny8
libfreetype6-dev 2.3.7-2+lenny7 => 2.3.7-2+lenny8

———————- dpkg status changes End ————————-

——————— httpd Begin ————————

Requests with error response codes
400 Bad Request
HTTP/1.1: 2 Time(s)
admin/scripts/setup.php: 2 Time(s)
401 Unauthorized


———————- vpopmail End ————————-

——————— Disk Space Begin ————————

Filesystem Size Used Avail Use% Mounted on
/dev/md0 222G 58G 154G 28% /

———————- Disk Space End ————————-

###################### Logwatch End #########################

The execution might take up from 10 to 20 seconds up to 10 or 20 minutes depending on the log files size and the CPU / RAM hardware on the machine where /var/log/… logs will be analyzed.

logwatch output can be easily mailed to a custom mail address using a crontab if the server runs a properly configured SMTP server. Using a cron like:

00 5 * * * /usr/sbin/logwatch | mail -s "$(hostname) log files for $(date)"

Here is time to make a note that logwatch is ported also to FreeBSD and is available from BSD’s port tree, from a port with path:

/usr/ports/security/logcheck

2. logcheck is another handy program, which does very similar job to logwatch . The “interesting” information it returns is a bit less than compared to logwatch

The good thing about logcheck is that by default it is made to mail every 1 hour a brief data summary which might be of an interest to the sys admin.
Logcheck is available for install on RedHat distros via yum and has existing package for Debian as well as a port for FreeBSD under the port location /usr/ports/security/logcheck

To install on logcheck on Debian:

debian:~# apt-get install logcheck
...

After installation I found it wise to change the default mailing time from each and every hour to just once per day to prevent my email from overfilling with “useless” mails.

This is done by editting the default cron tab installed by the package located in /etc/cron.d/logcheck

The default file looks like so:

# /etc/cron.d/logcheck: crontab entries for the logcheck package
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
@reboot logcheck if [ -x /usr/sbin/logcheck ]; then nice -n10 /usr/sbin/logcheck -R; fi
2 * * * * logcheck if [ -x /usr/sbin/logcheck ]; then nice -n10 /usr/sbin/logcheck; fi
# EOF

To change it run only once per day its content should looks something like:

# /etc/cron.d/logcheck: crontab entries for the logcheck package
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
@reboot logcheck if [ -x /usr/sbin/logcheck ]; then nice -n10 /usr/sbin/logcheck -R; fi
2 5 * * * logcheck if [ -x /usr/sbin/logcheck ]; then nice -n10 /usr/sbin/logcheck; fi
# EOF

Altering it that way the log summary interesting info analysis will be sent on mail every day in 05:02 a.m.
Changing the default email logcheck will ship its log analyzer report emails on deb based distros is done via editting the file:

/etc/logcheck/logcheck.conf

And changing the SENDMAILTO=”” variable to point to the appropriate admin email email addr.
 

Where does Debian GNU / Linux Apache + PHP stores session files?

Tuesday, November 22nd, 2011

In order to debug some PHP session problems on Debian, I needed to check the count of existing session files.
When PHP is compiled from source usually, by default sessions are stored in /tmp directory, however this is not the case on Debian.

Debian’s PHP session directory is different, there the sessions are stored in the directory:

/var/lib/php5

I’ve discovered the session directory location by reading Debian’s cron shell script, which delete session files on every 30 minutes.

Here is the file content:

debian~# cat /etc/cron.d/php5
# /etc/cron.d/php5: crontab fragment for php5
# This purges session files older than X, where X is defined in seconds
# as the largest value of session.gc_maxlifetime from all your php.ini
# files, or 24 minutes if not defined. See /usr/lib/php5/maxlifetime

# Look for and purge old sessions every 30 minutes
09,39 * * * * root [ -x /usr/lib/php5/maxlifetime ] &&
[ -d /var/lib/php5 ] && find /var/lib/php5/ -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete

To check the amount of existing PHP opened session files:

debian:~# ls -1 /var/lib/php5|wc -l
14049