Setting umask
You can setup umask in /etc/bashrc or /etc/profile file for all users. By default most Linux distro set it to 0022 (022) or 0002 (002).
Users themselves can set their umask by creating in their home directory a custom profile file.
Calculating umask
Task: Calculating The Final Permission For FILES
You can simply subtract the umask from the base permissions to determine the final permission for file as follows:
666 - 022 = 644
- File base permissions : 666
- umask value : 022
- subtract to get permissions of new file (666-022) : 644 (rw-r--r--)
Task: Calculating The Final Permission For DIRECTORIES
You can simply subtract the umask from the base permissions to determine the final permission for directory as follows:
777 - 022 = 755
- Directory base permissions : 777
- umask value : 022
- Subtract to get permissions of new directory (777-022) : 755 (rwxr-xr-x)
References
This seems to talk about the acl and mask issue - http://bsdwiki.reedmedia.net/wiki/View_and_modify_ACLs.html
First Google hit - http://www.cyberciti.biz/tips/understanding-linux-unix-umask-value-usage.html
Says it has examples - http://linuxaria.com/article/linux-shell-understanding-umask-with-examples?lang=en