php:: how long to tmp files stay?

Files uploaded through POST are deleted right after php script finishes its execution.

According to php.net: "The file will be deleted from the temporary directory at the end of the request if it has not been moved away or renamed."

For uploaded files, the manual states:

The file will be deleted from the temporary directory at the end of the request if it has not been moved away or renamed.

Files that are to be kept should therefore be moved to another location.

More generally, as your question title might imply, temporary folders are left to be cleaned up by the system. This is true when using functions like tempnam or tmpfile, or simply when writing to the temporary directory (see sys_get_temp_dir).

In Ubuntu, this is done at every system reboot, or at a time interval, as defined in /etc/default/rcS.

In some Red Hat based distros, it is done using the tmpwatch utility from a cronjob. In others, the /tmp partition is mounted using the tmpfs filesystem, which is similar to a RAM disk (therefore being cleaned when the computer shuts down).

Another known mechanism is a size threshold, which means that the temporary directory will be cleaned up from the older files when it reaches a certain size.