Permissions

When root user create any directory then default permission à 755
When root user create any file then default permission à 644
When other user create any directory then default permission à 775
When other user create any file then default permission à 664
Umask for root user à 022
Umask for other user à 002
chown //change ownership
chmod //modify permission
chgrp //change group for file or directory
chmod -R rwX <dir> //it will set rwx permission to parent directory and all child directory

1.1 Special Permission

For SUID

To Remove SUID

To Set SGID

To Remove SGID

When set on a directory, users with write access to the directory can only delete files they own in the directory.

# chmod o+t <dir> //to set sticky bit

# chmod o-t <dir> //to remove sticky bit

Default ACLs

Remove ACL