I am working on an upload script.
If a user uploads a file and it already exists I want to warn the user (this is all through ajax) and give them the option to replace it, or cancel.
Instead of moving the file, I was curious if I could just leave the file in tmp and pass back the path to that file in the ajax response.
If they user says overwrite the old file in that ajax request pass the path back to php which continues to work on the file.
For this to work however I need to know how long a file stays in php's tmp dir
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.
There are three variables that need to be set in PHP to make sure that Garbage Collection of the /tmp directory happens correctly and they are:
session.gc_maxlifetime = 21600
session.gc_probability = 1
session.gc_divisor = 100
Set session.gc_maxlifetime to be the number of seconds you want each tmp file to last before it's deleted. If you login to the admin in OpenCart, this is the number of seconds until you will automatically be logged out. For example to set half an hour, you would do 60 seconds times 30 minutes which would be a value of 1800 seconds.
The other two variables are related to when the Garbage Collector will run, and it's important that they are set to the values above if you're having problems with this.
More info here: https://www.antropy.co.uk/blog/opencart-php-session-tmp-files-filling-up/
来源：https://stackoverflow.com/questions/4653224/php-how-long-to-tmp-files-stay