Lec. 13 File Permissions and Ownership

Introduction to permissions
• Permissions allow users to protect files and directories • Three permissions types: read, write and execute • Permissions have different meaning on files vs directories
Files vs directories
Permission (Symbol)
Effect of File Effect on Directory
read (r) Allows for file contents to be read or copied.
Without execute permission on the directory, allows for a non-detailed listing of files. With execute permission, ls -l can provide a detailed listing.
write (w) Allows for contents to be modified or overwritten.
Allows for files to be added or removed from directory. For this permission to work, the directory must also have execute permission.
execute (x) Allows for file to be run as a process, although text script files require read permission, as well.
Allows user to change to the directory, if parent directories have execute permission, as well
Displaying permissions
• Permissions are displayed with ls -l command: $ ls -l /bin/ls -rwxr-xr-x 1 root root 118644 Apr 4 2014 /bin/ls
First character: file type (- for file, d for directory) Next 9 characters: permissions Next 1 character: # of links the file has to other files 1st “root”: file owner 2nd “root”: the primary group name the owner belongs to 118644: file size in bytes Apr 4 2014: date created or last modified /bin/ls: file or directory name