chmod - change file mode bits.
Add execute permission for the user:
chmod u+x my_file.txt
Add read permission for the user:
chmod u+r my_file.txt
Add write permission for the user:
chmod u+w my_file.txt
Removes read and write permissions for the user:
chmod u-rw my_file.txt
Add read, write and execute permissions for the group:
chmod g+rwx my_file.txt
Add multiple permission to a file:
chmod u+r,g+x my_file.txt
Add read, write and execute permissions for everyone:
chmod a+rwx my_file.txt