chmod Calculator
Convert between Unix file permission notations — octal (755), symbolic (rwxr-xr-x), and binary. Toggle permissions and preview the chmod command.
Common presets:
Permission Bits
Owner (u)7
Group (g)5
Others (o)5
Octal
Symbolic
rwxr-xr-x
Binary
111 101 101
Command
chmod 755 filename
How to Use chmod Calculator
- 1Enter an octal value (e.g., 755) or toggle the permission checkboxes.
- 2See the symbolic notation and numeric value update in real time.
- 3Copy the ready-to-use chmod command.
- 4Use the presets for common permission patterns.
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Frequently Asked Questions
What do the Unix permission bits mean?▾
Unix permissions have three sets for three principals: Owner (u), Group (g), and Others (o). Each set has three bits: Read (r = 4), Write (w = 2), Execute (x = 1). Octal notation adds the three bits: rwx = 7, rw- = 6, r-x = 5, r-- = 4, etc. chmod 755 means owner=rwx (7), group=r-x (5), others=r-x (5). For directories, the execute bit means "enter/list" permission.
What are the most common permission values?▾
644 (rw-r--r--) — standard file: owner can read/write, everyone else read-only. Typical for web server content files. 755 (rwxr-xr-x) — standard directory or executable: owner can do everything, everyone else can read and execute. 600 (rw-------) — private file: only owner can read/write. Typical for SSH keys and config files with secrets. 700 (rwx------) — private directory: only owner can access. 777 (rwxrwxrwx) — fully open: everyone can do everything. Avoid in production.
What is the sticky bit and setuid/setgid?▾
Unix has three special bits: Setuid (SUID, 4000) — when set on an executable, it runs with the file owner's privileges (used by sudo, passwd). Setgid (SGID, 2000) — on executables: runs with group privileges; on directories: new files inherit the directory's group. Sticky bit (1000) — on directories: only the file owner can delete their files (used on /tmp). Combined with standard permissions: chmod 1755 /tmp sets sticky + 755.
chmod symbolic vs octal — which should I use?▾
Octal (chmod 644 file) is explicit and sets all permissions at once — it is the most unambiguous and commonly used in scripts. Symbolic (chmod u+x file, chmod g-w file) modifies specific bits without changing others — useful when you want to add execute to the owner without knowing the current permissions. chmod a+r file adds read for all principals. chmod o= file removes all permissions for others.
How do I change permissions recursively?▾
Use chmod -R 755 /path to recursively set permissions on a directory and all its contents. Warning: applying the same permissions to files and directories is often wrong — directories need execute to be traversable. A better pattern uses find: find /path -type f -exec chmod 644 {} \; for files and find /path -type d -exec chmod 755 {} \; for directories.