CentOS Tmpwatch – When Does It Clear Files in /tmp

When the system boots and the harddrive is full, nothing can write to /tmp. So during init a tmpfs is created and mounted. This way your system can safely boot, because it can write to /tmp.

Free up disc space, and reboot your machine. (Or simply unmount /tmp, if you are sure nothing uses it).

Setting this value to 0 disables the setup., which I would expect carries the risk of init-failure, or being unable to log in to the system.

I think the answer by Nitesh B. is dangerous and should be avoided.

The de jure standard location for temporary files is given in the environment variable TMPDIR.

This variable shall represent a pathname of a directory made available for programs that need a place to create temporary files.

In fact, many systems do not define TMPDIR. The de facto standard location for temporary files is /tmp. So check TMPDIR, and if it is not set, use /tmp. In a shell script, you can use ${TMPDIR:-/tmp}, or if you find it more convenient,

if [ -z "$TMPDIR" ]; then TMPDIR=/tmp; fi

or to cope with set -u

: "${TMPDIR:=/tmp}"

You can assume that this location is writable, but it may be world-readable and world-writable, so:

• When you create a regular file, always make sure that you aren't overwriting an existing file, which might not belong to you. Don't use a shell redirection for this. It is not safe to test ownership separately because an adversary may move symbolic links around while your program is running to fool the checks. Additionally you can't rely on a particular name not existing; to prevent a concurrent program from creating a denial of service by creating a file with the same name just before you, use a random name. You can use the mktemp utility (widespread, present on GNU, BusyBox, BSD, but not POSIX) or the mkstemp C library function. Under the hood, open or creat must be called with the O_EXCL flag.
• You can create a directory with mkdir. This is secure against ownership trickery stealing, because that won't reuse an existing file, but it is prone to the same denial of service as regular files, so you should use a random name. mktemp -d is a fine way to do this.
• You can create a socket (there's no standard shell utility for that). Like the directory case, it is secure against ownership trickery but not against denial of service.
  Linux honors permissions on named sockets, but there are Unix variants that don't. This is why sockets in /tmp are usually created in subdirectories.

Programs that create a subdirectory of /tmp (or $TMPDIR if set) and create a named socket there include X11 servers, ssh-agent, gpg-agent, KDE, emacs, … (that's just the ones that exist on the machine where I'm posting this). As you can see, you'll be in good company.