Linux permissions control who can access files and directories. They’re assigned to users and groups, with each user potentially belonging to multiple groups. Being in a group grants specific access rights to files and directories associated with that group.
Permission Values
Number Permission Meaning 0---No permission 1--xExecute only 2-w-Write only 3-wxWrite and execute 4r--Read only 5r-xRead and execute 6rw-Read and write 7rwxFull access (read, write, execute)
Common Permission Combinations
Value Symbolic Description 755rwxr-xr-xOwner: full access; Group/Others: read & execute 644rw-r--r--Owner: read & write; Group/Others: read only 700rwx------Owner: full access; Group/Others: no access 777rwxrwxrwxEveryone has full access (use with caution)
Setting Permissions
# Numeric method chmod 755 file.txt # rwxr-xr-x
# Symbolic method chmod u+x script.sh # Add execute for owner chmod go-w file.txt # Remove write from group/others chmod -R 755 directory/ # Apply recursively to directory Checking Permissions
ls -l file.txt # List file permissions ls -ld directory/ # List directory permissions