Chmod calculator
Unix file permissions control owner, group, and others access with read (r=4), write (w=2), execute (x=1) bits. chmod 755 means rwxr-xr-x. Toggle checkboxes or enter octal to see symbolic form — essential when fixing deploy scripts and Docker volume permissions.
Owner
Group
Others
Octal
Output
chmod 644
rw-r--r--
How to use the chmod calculator
1. Toggle read/write/execute for owner, group, and others.
2. Read octal value (e.g. 644, 755, 600).
3. Copy symbolic equivalent chmod u=rw,go=r.
4. Apply on server: chmod 644 file.txt
Chmod examples
Web directory 755
rwxr-xr-x lets owner modify files; world can enter directory and read.
Secret env file 600
rw------- — only owner reads/writes .env with API keys.
Executable script 755
rwxr-xr-x on deploy.sh so cron user can execute.
When chmod calculator helps
• When learning Unix permission model.
• When Dockerfile COPY needs explicit numeric mode.
• When ls -l rwxr-xr-x output must map to octal for IaC template.
Beyond basic chmod
• When ACLs (setfacl) or SELinux contexts govern access — chmod alone insufficient.
• When Windows NTFS permissions — different model entirely.
• When setuid/setgid/sticky bits needed — extend beyond rwx triplet calculator.
Owner group others
Three triplets user/group/others — chmod affects which triplet applies to current user context on access check.
Least privilege
Start 640 for configs, 755 for public static assets, never 777 in production — world-writable is audit finding.
Docker and Kubernetes
Containers run as non-root USER — ensure numeric uid can read mounted secrets mode 440 or 400.
Symbolic chmod
u+x adds execute for user; go-w removes group/other write — incremental changes without recalculating octal.
Frequently asked questions
Octal digit meaning?
Sum r=4 w=2 x=1 per triplet — 7=rwx, 6=rw-, 5=r-x, 4=r--.
755 vs 775?
775 adds group write — shared dev team editing; 755 group read-only.
Recursive chmod -R?
Applies to directory tree — dangerous on wrong path; verify twice.
File vs directory execute?
x on directory means enter (cd); on file means run as program.
umask interaction?
Default file mode = creation mask minus umask — calculator shows target mode not umask.
Local tool?
Yes — reference calculator in browser.