MacOS – How to determine public temp directory on OS X to be write-accessible by www server

command linefoldersmacosscript

I've MAMP running httpd server as _www and I'd like to assign the temporary directory as part of the shell script (bash).

I've tried to use $TMPDIR as per these posts:

however it points to /var/folders/vp/tlt7xf791gl1_v56m0xdmrph0000gn/T/ and this folder has not necessary permissions, so Apache server can't create any files in there.

Based on this:

$ /usr/bin/stat -F $TMPDIR /tmp /private/tmp 
drwx------ 104 kenorb staff 3536 Oct 14 22:21:05 2015 /var/folders/vp/tlt7xf791gl1_v56m0xdmrph0000gn/T//
lrwxr-xr-x 1 root wheel 11 Apr  9 13:08:03 2014 /tmp@ -> private/tmp
drwxrwxrwt 112 root wheel 3808 Oct 14 22:12:04 2015 /private/tmp/

My www user which I care about:

$ id _www
uid=70(_www) gid=70(_www) groups=70(_www),12(everyone),61(localaccounts),401(com.apple.sharepoint.group.1),100(_lpoperator)

I can't use /tmp, because it's linked to my /private/tmp (which name states it's private).

Therefore how do I determine my correct temporary directory on OS X, so I and my httpd server can use it?

I don't want to hardcode value, as the script would be useless when used on different environments (e.g. on non-MAMP environment), so the location can vary.

Best Answer

I would write to /tmp (which is equivalent to writing to /private/tmp ) since it's writable by all users and not just administrative users. It's there for compatibility and for bonus points, your script can clean up files or cut them if they grow too large.

I don't have an authoritative reference to why /private was called that, but it's always been open to writing and isn't restricted like $TMPDIR is from non-admin users.

The real question is what user are you running apache - a member of the ADMIN group or just a normal non-admin user?

Apple documents this in the Secure Coding Guide with the admonition that writing files to publicly readable locations is inherently insecure and that it's better to place files in more protected locations that aren't readable by all users. See the Race Conditions and Secure File Operations section and this link on creating secure temporary files. By using the mkstemp POSIX call you ensure a unique file is created and can control access with umask.

Oddly (to me), mktemp when run by a non-admin user can still make a temp file in $TMPDIR so it's clearly using escalated privileges to hand off that more "secure" file to non-admin users. Pretty cool.

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