Quick Answer
Linux file permissions control who can read, write, or execute each file using three groups — owner, group, and other — represented by bits that combine into octal values like 644 or 755. Setting 777 on a web root lets any compromised PHP script overwrite your application. Setting 644 on a directory breaks navigation because directories need the execute bit to be entered. Converting between octal, symbolic notation like `rwxr-xr-x`, and the exact `chmod` command is where mistakes happen during incident response. This builder presents a permission matrix with Owner, Group, and Others checkboxes. Toggling read, write, and execute updates the octal value, symbolic string, and full `chmod` command live in the output panel. Preset buttons cover 644 for static files, 755 for directories and scripts, and 700 for private executables. Copy the complete command or just the mode. Runs entirely in your browser. Use it before deploying to production or when auditing a server where world-writable files could expose credentials.
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6 scripts + shared library + 52-page field guide. The production layer the free snippets don't cover.
Get the Toolkit →What does chmod 755 mean?
chmod 755 gives the owner full read, write, and execute permissions (7), and gives group and others read and execute but not write (5). It is the standard permission for directories and executable scripts on Linux web servers.
What is the difference between chmod 644 and chmod 755?
chmod 644 gives the owner read and write (no execute), and group and others read only. It is the correct permission for static files like HTML, CSS, and configuration files. chmod 755 adds execute permission, which is required for scripts and directories.
How do I make a bash script executable?
Run `chmod +x script.sh` to add execute permission without changing any other permissions. For a fresh script with no existing permissions, `chmod 755 script.sh` sets the standard owner-executable pattern used for system scripts.
What does the sticky bit do on a directory?
When the sticky bit is set on a directory (chmod +t or mode 1755), only the file owner or root can delete or rename files inside it — even if others have write access to the directory. The /tmp directory uses this to prevent users from deleting each other's temporary files.
intermediate · chmod
File Permissions Security Audit
World-writable files on a web server let any compromised script overwrite your application. find -perm 777 audits them and correct chmod 644/755 patterns restore safe permissions.
intermediate · ssh
SSH Key Setup Script
Password-based SSH is vulnerable to brute-force attacks and credential leaks on any internet-exposed server. Automates ssh-keygen -t ed25519 and ssh-copy-id to enable key-based auth in one run.