Understanding Linux umask on Redhat / Centos

Hold on Cowboy

This blog post is pretty old. Be careful with the information you find in here. The Times They Are A-Changin'

umask is linux’s way of determining default file/folder permissions when new files and folders are created. It’s a little odd in that the umask is subtracted from 777 for folders and 666 for files to get the correct permissions. I don’t claim to understand fully, but it just is.

What is your current umask? umask 0002

By default, normal users will get a umask of 0002 = 775 on a folder and 664 on a file. This equates to

-rwxrwxr—

for a file.

I had a user that had a set umask of 0022, but all other users had a umask of 0002. This puzzled me, I looked in the normal areas that you can override the umask

/etc/profile

and

~/.bashrc

but didn’t see anything obvious. Then looking in

/etc/passwd

I noticed this user had a groupid set to apache’s group (48). This was done for reasons outside this discussion.

So if a userid or groupid < 99 then umask = 0022 (more restrictive).

Resources: http://kbase.redhat.com/faq/docs/DOC-1373