The tmp directory and tmpwatch daemon

The tmp directory is normally used on Linux systems so that users or applications can store temporary information within it.

On Debian or Ubuntu distributions, the system cleans out all user data with each startup. On RHEL or CentOS 6, no operation is performed on that directory. But in version 5 of RHEL or CentOS, there was a great tool installed on the system by default, and utilized to periodically check the contents of the tmp directory: tmpwatch.

Tmpwatch is a cron job which takes care of removing files which have not been accessed for a period of time, or any file or folder that you configure. This operation is carried out based on guidelines which will be exposed later. The equivalent program on Debian/Ubuntu is tmpreaper, although you can compile tmpwatch perfectly for the aforementioned operating systems.

For the development of the present article, I am going to use CentOS 6.0 (32 bits).

[root@centos ~]# yum install tmpwatch

[root@centos ~]# cat /etc/cron.daily/tmpwatch 
#! /bin/sh
flags=-umc
/usr/sbin/tmpwatch "$flags" -x /tmp/.X11-unix -x /tmp/.XIM-unix \
        -x /tmp/.font-unix -x /tmp/.ICE-unix -x /tmp/.Test-unix \
        -X '/tmp/hsperfdata_*' 10d /tmp
/usr/sbin/tmpwatch "$flags" 30d /var/tmp
for d in /var/{cache/man,catman}/{cat?,X11R6/cat?,local/cat?}; do
    if [ -d "$d" ]; then
        /usr/sbin/tmpwatch "$flags" -f 30d "$d"
    fi
done

By taking a look at the script launched daily by the system, we may observe that tmpwatch acts on a series of directories (/tmp, /var/tmp, /var/local, etc.) by clearing out their contents. This task is accomplished based on certain events which have taken place throughout the last 10 or 30 days.

• -u (--atime): the decision to delete a file depends on its atime (access time).

• -m (--mtime): the decision to delete a file depends on its mtime (modification time).

• -c (--ctime): the decision to delete a file depends on its ctime (inode change time).

• -f (--force): removes files even whether root does not have write access.

By means of the '-x' option, we can leave out a specific file or directory that matches the pattern.