linux user management - change uid

Theory:

usermod -u <NEWUID> <LOGIN>    
groupmod -g <NEWGID> <GROUP>
find / -user <OLDUID> -exec chown -h <NEWUID> {} \;
find / -group <OLDGID> -exec chgrp -h <NEWGID> {} \;
usermod -g <NEWGID> <LOGIN>

Example:

#in recovery mode
find / -uid 1000 -exec chown -h 501 '{}' \+
usermod -g 501 pmichalec