Chmod Calculator
Calculate Unix file permissions.
chmod 755 filename
권한 상세
숫자 참고
Overview
A calculator that converts Unix/Linux file permissions between numeric (octal) and symbolic (rwx) notation. Accurately set file permissions for server management and deployment scripts.
Formula
chmod permission calculation: For each user category (Owner/Group/Others), sum read (r=4), write (w=2), and execute (x=1) permissions. Example: rwxr-xr-- → Owner (4+2+1=7), Group (4+0+1=5), Others (4+0+0=4) → 754. Special permissions: SUID (4000), SGID (2000), Sticky (1000). Example: chmod 4755 → SUID + rwxr-xr-x.
How to Use
- 1Enter a numeric mode (e.g., 755) or select permissions with checkboxes.
- 2Set permissions for Owner, Group, and Others individually.
- 3Add special permissions (SUID, SGID, Sticky bit) if needed.
- 4View the converted numeric/symbolic notation and chmod command.
Tips
- ✔Standard permissions for web server files are 644 (rw-r--r--) and 755 (rwxr-xr-x) for directories.
- ✔Avoid 777 (all permissions granted) for security reasons.
- ✔Use 755 or 750 for executables and scripts.
- ✔The .ssh directory requires 700 and private key files require 600 for SSH to work.
- ✔Understanding umask values helps predict default permissions for new files/directories.
FAQ
Q. What is the difference between chmod 755 and chmod 644?
755 (rwxr-xr-x) grants read/write/execute to the owner and read/execute to group and others. It is suitable for directories and executables. 644 (rw-r--r--) grants read/write to the owner and read-only to others, suitable for regular files.
Q. What are SUID, SGID, and Sticky bit?
SUID (Set User ID): Runs with the file owner's permissions (e.g., /usr/bin/passwd). SGID (Set Group ID): Runs with the file group's permissions, or in directories, new files inherit the parent's group. Sticky bit: In directories, only the file owner can delete files (e.g., /tmp).
Q. What is umask?
umask is a mask that specifies which permissions to remove from the default permissions of newly created files/directories. For example, with umask 022, new files are created with 644 (666−022) and new directories with 755 (777−022).
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