Archive for the ‘Debian’ Category
Get the name of the newest file in a directory on the linux shell
If you have a directory with many files (a few thousand in my case) and need to know which one is the newest, then the following command might be useful. It returns the name and details of the newest file in a directory where it is executed:
ls -tl | sed -n 2p
Reduce load of backup scripts with nice and ionice
Runing a nightly backup script on a server system like a webhosting server can produce high load and longer latencys for other processes, e.g. HTML or .php pages load slow during backup because the backup script takes too much I/O or CPU resources.
On Linux systems there are two shell utilitys available to set the I/O and CPU Scheduling for a appliaction or script. The utilitys are named nice and ionice.
Reduce the I/O priority of the script “/usr/local/bin/backup.sh” so that it does not disrupt other processes:
/usr/bin/ionice -c2 -n7 /usr/local/bin/backup.sh
The -n parameter must be between 0 and 7, where lower numbers mean higher priority.
To reduce the CPU priority, use the command nice:
/usr/bin/nice -n 19 /usr/local/bin/backup.sh
The -n parameter can range from -20 to 19, where lower numbers mean higher priority
Nice and ionice can also be combined, to run a script at low I/O and CPU priority:
/usr/bin/nice -n 19 /usr/bin/ionice -c2 -n7 /usr/local/bin/backup.sh
Disable quota for a Linux user or group on the shell
Linux user quotas can be edited with the commands edquota or setquota on the shell. While edquota opens the quota settings in a editor like vim, setquota allows you to specify the quota settings on the commandline.
Example for disabling the quota for the user “testuser”:
setquota -u testuser 0 0 0 0 -a
Example for disabling quota for the group “testgroup”:
setquota -g testgroup 0 0 0 0 -a
Prevent DOS attacks on apache webserver for DEBIAN linux with mod_evasive
The following guide explains the installation of the apache module “mod_evasive”. Mod_evasive tracks the number of requests of files at the apache webserver and blocks the delivery in case that a certain limit has been reached.
Installation
apt-get install libapache2-mod-evasive
Create the log directory for mod_evasive
mkdir -p /var/log/apache2/evasive
chown -R www-data:root /var/log/apache2/evasive
Now we add the configuration for the module at the end of the file /etc/apache2/mods-available/mod-evasive.load
vi /etc/apache2/mods-available/mod-evasive.load
so that it looks like this:
LoadModule evasive20_module /usr/lib/apache2/modules/mod_evasive20.so
DOSHashTableSize 3097
DOSPageCount 2
DOSSiteCount 50
DOSPageInterval 5
DOSSiteInterval 1
DOSBlockingPeriod 10
DOSLogDir “/var/log/apache2/evasive”
and restart apache:
/etc/init.d/apache2 restart
How to change the language of AWStats statistics on Debian Linux (ISPConfig 3)
To change the language of the website statistics generated by AWStats on a Debian Linux server to e.g. german (de), edit the /etc/awstats/awstats.conf file:
nano /etc/awstats/awstats.conf
and change the value of the “Lang” variable. To change the languge to e.g. German, cahnge:
Lang=”auto”
to
Lang=”de”
The website statistics are generated nightly on a ISPConfig 3 server, so it may take up to 24 hours until the statistics will show up in German language.
Thanks to PlaNet Fox for this FAQ.
Reconfigure rkhunter to avoid false positive warnings on Debian 5.0
When you run rkhunter on Debian Linux, you might get a warning when rkhunter is checking for hidden files and directories that some Hiffen files were found in /proc. A closer investigation in rkhunter might bring up the filenames /dev/.static, /dev/.udev and /dev/.initramfs which are normal files on Debian and not related to a attack on your system. The warnings in rkhunter.log are:
[10:21:40] Warning: Hidden directory found: /dev/.static
[10:21:40] Warning: Hidden directory found: /dev/.udev
[10:21:40] Warning: Hidden directory found: /dev/.initramfs
To avoid these warnings, you can reconfigure rkhunter to ignore these files by editing the rkhunter.conf file:
vi /etc/rkhunter.conf
and remove the # in fron of the following lines:
ALLOWHIDDENDIR=/dev/.udev
ALLOWHIDDENDIR=/dev/.static
ALLOWHIDDENDIR=/dev/.initramfs
Solve the warning: connect to mysql server 127.0.0.1: Too many connections
If you get the error message “connect to mysql server 127.0.0.1: Too many connections” in a log file, e.g. the mail.log file, then the max. number of mysql database connections on your server is reached. To increase the max. number of simultanious connections, edit the MySQL my.cnf file:
vi /etc/mysql/my.cnf
and add or change the lines for mysql max_connections and max_user_connections in the [mysqld] section of the my.cnf file:
[mysqld]
……
max_connections = 500
max_user_connections = 500
…….
How to solve the PHP XCache error: /dev/zero: No space left on device
If you get the error “/dev/zero: No space left on device” in the apache error.log on a OpenVZ virtual machine, then the shared memory size in the xcache.ini is too high or the xcache.mm_path is set wrong.
Edit the file /etc/php5/conf.d/xcache.ini
vi /etc/php5/conf.d/xcache.ini
and check the mm_path. On a OpenVZ virtual machine it should be set to “/tmp/xcache” as /dev/zero might not work correctly in a virtual machine:
xcache.mmap_path = “/tmp/xcache”
Then restart apache2:
/etc/init.d/apache2 restart
and check if the error has been resolved.
If the roor still occurs after some time, you will have to reduce the xcache.size.
Edite the xcache.ini file:
vi /etc/php5/conf.d/xcache.ini
and set xcache.size to e.g. 8 MB
xcache.size = 8M
Then restart apache2:
/etc/init.d/apache2 restart
How to disable spamfilter- and antivirus functions in ISPConfig 3
If you use a mailserver wil very low ram (< 500 MB) and a slow CPU then it might be nescessary to disable the spam- and antivirus filter functions in ISPConfig 3 as amavisd and clamav might be too heavy for your server hardware. The steps to disable clamav and amavisd are:
Edit postfix main.cf file
vi /etc/postfix/main.cf
and comment out these lines by adding a “#” in front of them:
# content_filter = amavis:[127.0.0.1]:10024
# receive_override_options = no_address_mappings
Then restart postfix:
/etc/init.d/postfix restart
Now stop and disable the services. The following commands are for Debian and Ubuntu, the commands for other Linux distributions may vary
/etc/init.d/clamav-daemon stop
/etc/init.d/clamav-freshclam stop
/etc/init.d/amavis stop
update-rc.d -f clamav-daemon remove
update-rc.d -f clamav-freshclam remove
update-rc.d -f amavis remove
P The normal mail receive and send functions will still work after this modification. But please be aware that disabling amavisd and clamav will disable all spam- and antivirus filtering so that the spamfiltering options that can be configured in the ispconfig interface will have any effect on mail delivery and no spam and viruses will get filtered.
The changes in postfix main.cf will get overwitten by a ispconfig software update when you select to reconfigure services during upadte, so you should comment out the lines again after you install a ispconfig update.
How to build a pure-ftpd Debian package for OpenVZ virtual machines (without capabilities enabled)
The pure-ftpd package that comes with Debian 5.0 (Lenny) does not start in a OpenVZ virtual machine as it is compiled with “capabilities”. This tutorial describes the steps to build a pure-ftpd Debian package with capabilities disabled:
Make a temporary directory
mkdir /usr/src/pure-ftpd
cd /usr/src/pure-ftpd
Download the source package for pure-ftpd
apt-get source pure-ftpd
apt-get build-dep pure-ftpd
Edit the rules file and add the switch “–without-capabilities”
cd pure-ftpd-1.0.21/debian
nano rules
Change the line:
optflags=–with-everything –with-largefile –with-pam –with-privsep –with-tls
to (one Line!):
optflags=–with-everything –with-largefile –with-pam –with-privsep –with-tls –without-capabilities
Build the Debian (.deb) package
cd ..
dpkg-buildpackage -uc -b
and install it
cd ..
dpkg -i pure-ftpd-common_1.0.21-11.4_all.deb pure-ftpd-mysql_1.0.21-11.4_i386.deb
/etc/init.d/pure-ftpd-mysql restart
To prevent that apt overwrites these manually compiled packages with the default packages from the Debian repositorys, execute these commands:
echo ‘pure-ftpd-common hold’ | dpkg –set-selections
echo ‘pure-ftpd-mysql hold’ | dpkg –set-selections
This tutorial is based on the german tutorial from planet_fox