Vicky's server guides » General linux admin

Perl update conflict in yum

vicky — Fri, 13 Jan 2012 16:50:44 +0000

Have you ever had problem updating perl via yum and yum spitting a conflict error message at you? I’ve met this problem on few CentOS 5 boxes of mine and thought I share the solution.

I happens on 64bit boxes and the error is for example like this

file /usr/share/man/man1/splain.1.gz from install of perl-5.8.8-32.el5_7.6.x86_64 conflicts with file from package perl-5.8.8-32.el5_6.3.i386
file /usr/share/man/man1/xsubpp.1.gz from install of perl-5.8.8-32.el5_7.6.x86_64 conflicts with file from package perl-5.8.8-32.el5_6.3.i386
file /usr/share/man/man3/CGI.3pm.gz from install of perl-5.8.8-32.el5_7.6.x86_64 conflicts with file from package perl-5.8.8-32.el5_6.3.i386

Obviously it is a problem of having a i386 version along the 64bit. First you need to remove the i386 version and then install perl again. You can do it by executing this command:

yum -y remove perl.i386 && yum -y install perl

It should work and you end up with a correct installation of perl. Until the next update

Add user to wheel group

vicky — Mon, 06 Jun 2011 07:37:12 +0000

If you are on cpanel (or any other centos server) and need the security feature that root cannot log in via ssh (I will cover this elsewhere) you can do it by adding new user by using these commands:

# adduser testuser
# passwd testuser

that will create the user “testuser” and prompts you to enter his password

With this you would not be able to su to root, therefore you need to add this user to wheel group by using command:

# usermod -f wheel testuser

Voila, now user “testuser” will be able to su – to root and you can disable direct root login in your ssh configuration.

boincmgr: error while loading shared libraries

vicky — Sun, 21 Nov 2010 13:13:35 +0000

Do you use your spare server power to compute BOINC projects? Seti@Home or MilkyWay or some others ?

You surely encountered error on CentOS 5 or RHEL 5 these errors:

./boincmgr: error while loading shared libraries: libXcomposite.so.1: cannot open shared object file: No such file or directory
./boincmgr: error while loading shared libraries: libXdamage.so.1: cannot open shared object file: No such file or directory
The cure is actually pretty easy, you just need to install the missing libraries

yum install libXcomposite libXdamage

And your problem should be vanished.. Also, you may need these libraries, but those should be installed by default: zlib, openssl, curl-devel

Happy computing

My nginx installation procedure

admin — Thu, 14 Jan 2010 16:47:46 +0000

I really started to like nginx web server, and here is my procedure step by step how to install this server on CentOS 5.4

yum install gcc pcre-devel openssl-devel wget http://nginx.org/download/nginx-0.7.65.tar.gz && tar xvfz nginx-0.7.65.tar.gz ./configure --prefix=/usr/local/nginx --with-http_stub_status_module --with-http_gzip_static_module make make install ln -s /usr/local/nginx/conf /etc/nginx ln -s /usr/local/nginx/logs /var/log/nginx ln -s /usr/local/nginx/sbin/nginx /usr/sbin/nginx

Then grab this init script for red hat from http://wiki.nginx.org/RedHatNginxInitScript and put it in /etc/init.d/nginx file. Chmod 755 the file and you are ready.

Audit still logging even when stoped

vicky — Tue, 10 Nov 2009 17:36:08 +0000

I had strange problem on one of my CentOS 5.4 servers. I stoped auditd service and disables SElinux, the server, however, was still logging all those annoying things like

Nov 10 18:27:01 server kernel: type=1105 audit(1257874021.909:87975): user pid=27986 uid=0 auid=0 msg=’PAM: session open acct=”root” : exe=”/usr/sbin/crond” (hostname=?, addr=?, terminal=cron res=success)’
Nov 10 18:27:02 server kernel: type=1104 audit(1257874022.828:87976): user pid=27986 uid=0 auid=0 msg=’PAM: setcred acct=”root” : exe=”/usr/sbin/crond” (hostname=?, addr=?, terminal=cron res=success)’

into /var/log/messages log, filling it up with garbage.

After some time spent investigating I fixed it. I edited /etc/audit/audit.rules and replaced line

-D

with this line

-e 0

After that I started auditd service, stopped it and no more logs in /var/log/messages

Show line numbers in vi or vim

vicky — Thu, 05 Nov 2009 14:19:00 +0000

Have you ever wondered how to show line numbers in vi or vim while editing file? I do that always when I patch some software or install MODs that come with “go to line xxx and rewrite this…”. And the solution is really simple.

In vi/vim type :set number to show line numbers and :set nonumber to hide line numbers.

proftpd show hidden files

vicky — Sun, 08 Mar 2009 19:04:38 +0000

Not seeing hidden linux files ( dot beginning files) in your ftp you can enable this option in your ftp client. (show linux hidden files). It it does not work you can force your linux ftp server to show them via this command in /etc/proftpd.conf

ListOptions -a

Put it into the conf file and restart proftpd service.

Turn on syntax highlighting in vi/vim

vicky — Sun, 01 Mar 2009 23:27:34 +0000

I recently got to administer a few linux boxes and wondered why vi does not show colors when I edit files. Some servers did it, some did not. It was differently set up by datacenter images and I really did not have time to investigate.

Now it just annoyed me because I could not find few syntax errors on one server and here is the solution.

Open up some file in vi or vim and hit ESC, then type “:syntax on” and the magic happens… let there be color

If you do like it without color, type “:syntax off”

Speeding up apache by mod_deflate and mod_expires

vicky — Wed, 05 Nov 2008 11:40:24 +0000

Here is how I speed up apache by compressing pages with mod_deflate module and setting higher cache expiration times in mod_expires module. Here is how…

put this in your apache config:

# compress html, plain text, css and javascript
AddOutputFilterByType DEFLATE text/html text/plain text/css text/javascript application/x-javascript
# avoid problems in known-to-be-problematic browsers
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

ExpiresActive On
ExpiresDefault A300
ExpiresByType image/x-icon A2592000
ExpiresByType application/x-javascript A3600
ExpiresByType text/css A3600
ExpiresByType image/gif A604800
ExpiresByType image/png A604800
ExpiresByType image/jpeg A604800
ExpiresByType text/plain A300
ExpiresByType application/x-shockwave-flash A604800
ExpiresByType video/x-flv A2592000
ExpiresByType application/pdf A300
ExpiresByType text/html A300

Times are in seconds. There are many variations how to set the time, read apache manual for further info.

Hope it helps to speed up your sites and save some bandwidth.

Disable cron email alert

vicky — Tue, 14 Oct 2008 14:12:35 +0000

Ever wondered how to disable the email alert sent when cron is executed? Easy help, there are various ways to achieve this, so feel free to use the one you like the best. They all work, though.

However, there are two principles – one to send the email to /dev/null and other one disable it by cron EMAILTO directive.

Redirect to /dev/null is used in these ways:

>/dev/null 2>&1.
or
&> /dev/null

Those need to be added at the end of your crontab entry, like this:

0 1 * * * /path/yourscript.sh >/dev/null 2>&1

Or, as I said using EMAILTO would look in your crontab file like this:

EMAILTO=""

It should be placed on top of either /etc/crontab or you can define cron entries by executing: crontab -e

I hope this was helpfull…