File permissions in Unix and Linux are represented by a three-digit octal number. Each digit can be a value from 0 to 7, representing different levels of permission. The three digits are assigned to:
Each digit is a sum of the following values:
| Number | Permission | Symbol |
|---|---|---|
| 0 | No Permission | — |
| 1 | Execute | –x |
| 2 | Write | -w- |
| 4 | Read | r– |
These values can be combined to form other permissions:
| Number | Permission | Symbol |
|---|---|---|
| 3 | Write and Execute | -wx |
| 5 | Read and Execute | r-x |
| 6 | Read and Write | rw- |
| 7 | Read, Write, Execute | rwx |
777: Read, write, and execute permissions for user, group, and others.
chmod 777 filename
Permissions: rwxrwxrwx
755: Read, write, and execute permissions for user; read and execute permissions for group and others.
chmod 755 filename
Permissions: rwxr-xr-x
644: Read and write permissions for user; read-only permissions for group and others.
chmod 644 filename
Permissions: rw-r--r--
| Number | User (Owner) | Group | Others | Symbol |
|---|---|---|---|---|
| 0 | No Permission | No Permission | No Permission | — |
| 1 | Execute | Execute | Execute | –x |
| 2 | Write | Write | Write | -w- |
| 3 | Write and Execute | Write and Execute | Write and Execute | -wx |
| 4 | Read | Read | Read | r– |
| 5 | Read and Execute | Read and Execute | Read and Execute | r-x |
| 6 | Read and Write | Read and Write | Read and Write | rw- |
| 7 | Read, Write, Execute | Read, Write, Execute | Read, Write, Execute | rwx |