Setting ACL (Access Control List)

Add permissions to some user:
# setfacl -m "u:<username>:<permissions>" <filename>
or
# setfacl -m "u:<uid>:<permissions>"  <filename>

Example:
# setfacl -m "u:johny:r-x" abc

Add permissions to some group:
# setfacl -m "g:<groupname>:<permissions>" <filename>
or
# setfacl -m "g:<gid>:<permissions>" <filename>

Check permissions
# getfacl <filename>

To apply it recursively:
# setfacl -R -m u:colleague:rwx <filename>

Remove all extended ACL entries:
# setfacl -b <filename>

Output of ls command:
# ls -l /dev/audio
crw-rw----+ 1 root audio 14, 4 nov.   9 12:49 /dev/audio