巧匠Developer Cheatsheet

chmod Cheatsheet - Linux File Permission Reference

Scripts always ask for chmod +x, and wrong log-directory permissions break everything — understanding the permission quartet of owner/group/others plus the special bits makes most permission problems obvious at a glance. This table pairs numeric and symbolic forms, covering common combinations and when to use (and the risks of) SUID, SGID, and the sticky bit.

SysOps·37 commands·Last updated 2026-07-21
chmodPermissionslinux

Permission Bits 6

r (read)
Read permission, value 4
w (write)
Write permission, value 2
x (execute)
Execute permission, value 1
- (no permission)
No permission, value 0
u g o
User (owner) / Group / Others
a
All, equivalent to ugo

Numeric Mode 6

chmod 755 file
rwxr-xr-x (owner full, others read+execute)
chmod 644 file
rw-r--r-- (owner read+write, others read-only)
chmod 700 file
rwx------ (owner only)
chmod 600 file
rw------- (owner read+write, common for private keys)
chmod 777 file
rwxrwxrwx (everyone full — dangerous!)
chmod 750 dir
rwxr-x--- (owner full, group read+execute)

Symbolic Mode 6

chmod u+x file
Add execute for the owner
chmod go-w file
Remove write for group and others
chmod a+r file
Add read for everyone
chmod u=rw,go=r file
Set owner read+write, others read-only
chmod +x script.sh
Add execute for everyone (defaults to a when omitted)
chmod -R 755 dir/
Recursively change directory permissions

Special Permissions 6

chmod u+s file (4755)
SUID: runs with the owner's identity
chmod g+s dir (2755)
SGID: new files in the dir inherit its group
chmod +t dir (1777)
Sticky: only the owner can delete (e.g. /tmp)
chmod 4755 file
Set SUID in numeric mode
chmod 2755 dir
Set SGID in numeric mode
chmod 1777 dir
Set Sticky in numeric mode

Common Patterns 6

644
Regular files (owner rw, others r)
755
Executables and directories
600
Private key files (SSH, SSL)
640
Config files (owner rw, group r)
700
Private directories (owner only)
750
Shared directories (owner full, group r-x)

Tips

  • Numeric mode: r=4, w=2, x=1; sum them for the value (e.g. rwx = 4+2+1 = 7).
  • A directory's x means you can enter it (cd); without x, even r won't let you in.
  • SUID has no effect on scripts (only on binaries) and is a security risk — use with caution.

Related Cheatsheets

6 related cheatsheets

Linux Troubleshooting Cheatsheet - System Fault Diagnosis Command ReferenceA one-stop Linux troubleshooting reference organized by process/load, port/network, disk/memory, and logs/services, helping you quickly spot performance bottlenecks, connection anomalies, and resource hogs during live incidents.Vim Cheatsheet - Editor Command ReferenceA Vim operation reference covering cursor motion, text editing, search and replace, visual mode, and save/exit, aimed at developers and operators editing files on a server, including real-world tricks such as batch replacement and saving with sudo.Systemd Cheatsheet - Systemd Service Management Command ReferenceA Systemd service-management reference covering start/stop and boot-enabling, journalctl log viewing, timer scheduling, targets and runlevels, and resource limits, with the differences between easily-confused pairs such as reload vs restart and mask vs disable.Cron Cheatsheet - Cron Expression & Task Scheduling ReferenceA Cron scheduling reference spanning the 5-field expression format, special characters and time macros, common examples, environment variables, and troubleshooting, flagging frequent pitfalls such as the OR relationship between day-of-month and day-of-week and the minimal default PATH.CI/CD Commands Cheatsheet - CI/CD Pipeline Debugging ReferenceA debugging reference for GitHub Actions, GitLab CI, and Jenkins pipelines, covering job reruns and log extraction, runner online status, cache and disk usage, and local reproduction with act or gitlab-runner exec.MQ Commands Cheatsheet - Kafka/RabbitMQ/RocketMQ ReferenceAn MQ operations reference for Kafka, RabbitMQ, RocketMQ, and Redis Pub/Sub, focused on the four high-frequency scenarios of locating consumer backlog, hunting connection leaks, diagnosing cluster state, and benchmarking throughput.

Official References

Each command links to its official documentation below, so you can verify the latest usage and read deeper.

Maintained by LaoHand

Publicly updated on Jul 21, 2026, continuously proofread against official docs.

Contact Us

Wrong command or description? Send us corrections, business inquiries or product feedback by email.

Contact Us