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# /tmp
**/tmp** is the system-wide directory for temporary files. Any process can create files here. The kernel cleans it on reboot; many distributions also run a periodic cleanup of files older than a few days. On most modern systems `/tmp` is a **tmpfs** mount, meaning it lives entirely in RAM (and swap) rather than on disk — writes to `/tmp` never touch the filesystem and are lost on reboot.

```sh
# common uses
mktemp              # create a unique temporary file, returns the path
mktemp -d           # create a unique temporary directory
mktemp /tmp/proc.XXXXXX  # XXXXXX is replaced with a random suffix
```

`/tmp` is world-writable: every user and process can create files in it. To prevent one user from hijacking another's temporary files, the **sticky bit** is set on the directory (`drwxrwxrwt`). The sticky bit means that only the file's owner (and root) can delete or rename it, even though everyone has write permission on the directory itself.

For files that should survive across reboots, use `/var/tmp` instead. The convention is that `/tmp` can be cleared at any time, while `/var/tmp` persists until explicitly removed. Daemons and long-running services should use `/var/tmp` for work files they expect to pick up after a restart.