Permissions Command Practice
chmod sets who can read, write, or execute a path; chown sets which user and group own it. This track drills octal modes (755, 644), symbolic edits (u+x, go=), and chown user:group forms as separate answers — an octal is wrong on a symbolic prompt. The same commands show up on SSH keys, web roots, and shared project directories.
Command Reference
numeric
| Command | Description |
|---|---|
chmod 600 <file> | Set octal mode 600 so only the owner can read and write. |
chmod 700 <file> | Set octal mode 700 so only the owner has read, write, and execute. |
chmod 755 <file> | Set octal mode 755 so the owner has rwx and group and others have rx only. |
chmod 644 <file> | Set octal mode 644 so the owner can read and write while group and others can only read. |
chmod 777 <file> | Set octal mode 777 so every class can read, write, and execute. |
chmod 664 <file> | Set octal mode 664 so owner and group can read and write, and others can only read. |
chmod 660 <file> | Set octal mode 660 so owner and group can read and write, and others have no access. |
chmod 400 <file> | Set octal mode 400 so only the owner can read the file. |
chmod 775 <file> | Set octal mode 775 so owner and group have rwx and others have rx. |
chmod -R 755 <dir> | Recursively set octal mode 755 on a directory and everything under it. |
chmod -R 644 <dir> | Recursively set octal mode 644 on a directory tree (typical files-only web layout). |
chmod 500 <file> | Set octal mode 500 so only the owner can read and execute, with no write bit. |
chmod 754 <file> | Set octal mode 754 so the owner has rwx, the group has rx, and others have read only. |
find <dir> -type f -exec chmod 644 {} \; | Find all files within a path and set their permissions to octal 644. |
find <dir> -type d -exec chmod 755 {} \; | Find all directories within a path and set their permissions to octal 755. |
symbolic
| Command | Description |
|---|---|
chmod +x <file> | Add the execute bit with no class letter (umask may still block some classes). |
chmod u+x <file> | Add the execute bit for the owner only, using symbolic notation. |
chmod u-x <file> | Remove the execute bit from the owner using symbolic notation. |
chmod a-x <file> | Remove the execute bit from every class using symbolic notation. |
chmod a+r <file> | Add the read bit for every class using symbolic notation. |
chmod a+x <file> | Add the execute bit for user, group, and other, ignoring umask. |
chmod go+rw <file> | Add read and write for group and others, leaving the owner bits unchanged. |
chmod o-rw <file> | Remove read and write from others using symbolic notation. |
chmod g-rx <file> | Remove read and execute from the group using symbolic notation. |
chmod go= <file> | Clear every group and other bit (set those classes to none) using symbolic notation. |
chmod o= <file> | Clear every other-class bit using symbolic notation, leaving owner and group alone. |
chmod a=rwx <file> | Set all classes (user, group, others) to read, write, and execute using symbolic notation. |
chmod g-rx,o+rx <file> | Remove read and execute from the group and add them to others, in one symbolic chmod. |
chmod o=g <file> | Copy the group's current bits onto others using symbolic notation. |
chmod u=rwx,g=rx,o=r <file> | Assign an exact symbolic mask equivalent to 754: owner rwx, group rx, others read-only. |
chmod u=rw,g=,o= <file> | Assign an exact symbolic mask equivalent to 600: owner read/write, clear group and others. |
chmod u=rw,g=rw,o=r <file> | Assign an exact symbolic mask equivalent to 664: owner and group read/write, others read-only. |
chmod u=rwx,g=rx,o= <file> | Assign an exact symbolic mask: owner rwx, group rx, others none. |
chmod -R g+w,o+w <dir> | Recursively add write for group and others using symbolic notation. |
chmod =rwx,g+s <file> | Set rwx for every class and turn on the setgid bit, using symbolic notation. |
chown
| Command | Description |
|---|---|
chown <user> <file> | Change only the owning user of a file, leaving the group unchanged. |
chown <user>:<group> <file> | Set both owning user and group on a file. |
chown <user>: <file> | Set the owner to a user and set the group to that same user name. |
chown :<group> <file> | Change only the owning group, leaving the user unchanged. |
chown -R <user> <dir> | Recursively change the owning user of a directory and its contents. |
chown -R <user>:<group> <dir> | Recursively set both owning user and group on a directory tree. |
chown -h <user> <file> | Change the owner of a symlink itself, not the target it points to. |
chown --reference <file> <file> | Copy user and group ownership from a reference file onto another path. |
Key Use Cases
- Set octal 755 on a script so others can run it but only the owner can write
- Add execute for the owner with u+x without rewriting group or other bits
- Clear all group and other access with go=
- Recursively apply octal 644 to a directory tree
- Give a path to another user and group with chown user:group
- Change ownership of a symlink itself, not the target
Frequently Asked Questions
Is chmod 755 the same answer as chmod u=rwx,g=rx,o=rx?
They can produce the same bits, but this track scores notation. An octal is wrong on a symbolic prompt and a u=rwx form is wrong on an octal prompt.
Why isn't chmod +x the same as chmod a+x?
With no class letter, chmod acts like a but honors umask, so some bits may stay off. a+x sets execute for user, group, and other regardless of umask.
How do I change only the group with chown?
chown :<group> <file> leaves the owner alone. chown <user>: sets both owner and group to that user name.
What does g+s do on a file or directory?
It sets the setgid bit. New files in that directory inherit the directory's group. =rwx,g+s is a different command than plain 777.
Ready to master Permissions commands?
Test your muscle memory with our spaced-repetition quiz system. Free forever.