Cron job to delete files older than 3 days

Question

I need to remove files older than 3 days with a cron job in 3 different directories. (these 3 directories are children of a parent directory /a/b/c/1 & /a/b/c/2 & /a/b/c/3) Can this be done with one line in the crontab?

Solution 1

This is easy enough (although note that this goes by a modification time more than 3 days ago since a creation time is only available on certain filesystems with special tools):

find /a/b/c/1 /a/b/c/2 -type f -mtime +3 #-delete

Remove the # before the -delete once you are sure that it is finding the files you want to remove.

To have it run by cron, I would probably just create an executable script (add a shebang - #!bin/sh to the top line of the file and make executable with chmod a+x), then put it in an appropriate cron directory like /etc/cron.daily or /etc/cron.weekly. Provided of course that you do not need a more specific schedule and that these directories exist on your distro.

Update

As noted below, the -delete option for find isn't very portable. A POSIX compatible approach would be:

find /a/b/c/1 /a/b/c/2 -type f -mtime +3 #-exec rm {} +

Again remove the # when you are sure you have the right files.

Update2

To quote from Stéphane Chazelas comment below:

Note that -exec rm {} + has race condition vulnerabilities which -delete (where available) doesn't have. So don't use it on directories that are writeable by others. Some finds also have a -execdir that mitigates against those vulnerabilities.

Solution 2

You would be much better off using tmpwatch

tmpwatch recursively removes files which haven't been accessed for a given time. Normally, it's used to clean up directories which are used for temporary holding space such as /tmp.

Comments

[KingKongFrog]

Thanks! Is there a way to specify the parent directory and then the child directories so the /a/b/c/ doesn't have to be specified for every option?

[Graeme]

Sure, in a POSIX shell you can do /a/b/c/[12], but this is only really appropriate if the subdirectories have single letter names. In bash you can do /a/b/c/{1,2}. Of course then the bang line for a script would have to be #!/bin/bash or if you are using crontab, you need to make sure it is configured to use bash (I don't really recommend changing it if it isn't).

[Stéphane Chazelas]

brace expansion is a csh feature and is also supported by ksh, bash, zsh and fish so you have a wide choice of shells. ksh, bash and zsh also have alternation operators in their globs. Note that -exec rm {} + has race condition vulnerabilities which -delete (where available) doesn't have. So don't use it on directories that are writeable by others. Some finds also have a -execdir that mitigates against those vulnerabilities.

[cjaphe]

Does rm -f not handle errors silently, thereby handling any possible race condition with -exec?

[Wildcard]

@StéphaneChazelas, could you please link to a more full explanation of the race condition you mentioned? I'm interested.

[Stéphane Chazelas]

@Wildcard, see for instance Why did find with -delete erase the files in my /save/ directory when find without delete was not able to locate them? or how to delete (or keep) certain file extensions using busybox find?

[Jaap]

tmpwatch has been forked to tmpreaper, which (at least on Debian) seems to be it's replacement.