'u' means to change the permissions for the user (owner) of the file, '+' means to set a permission, and 's' means to set/remove the user or group ID on the file. From the man pages of chmod(1) ('man 1 chmod'):
Code:
The letters `rwxXstugo' select the new permissions for the affected users: read (r), write (w), execute
(or access for directories) (x), execute only if the file is a directory or already has execute permis-
sion for some user (X), set user or group ID on execution (s), sticky bit (t), the permissions that the
user who owns the file currently has for it (u), the permissions that other users in the file's group
have for it (g), and the permissions that other users not in the file's group have for it (o). (Thus,
chmod g-s file' removes the set-group-ID (sgid) bit, `chmod ug+s file' sets both the suid and sgid
bits, while `chmod o+s file' does nothing.)
