Linux permissions: ls -l and chmod

Simulation · Linux permissions [5.2.D.2, 5.2.D.3, 5.2.D.6, 5.2.D.7]

Permissions lab: set rwx with chmod

You are the system administrator for a clinic's Linux file server. Every file has three sets of permissions, always in the order owner, group, others, and each set is always read, write, execute.

admin@clinic-fs:/srv/clinic$ ls -l
total 60
-rwxrwxrwx 1 itadmin it        912 Nov  8 17:40 backup.sh
-rwxrwxrwx 1 itadmin it        604 Nov  8 17:41 kiosk.sh
-rw-rw-rw- 1 records doctors 48211 Nov  9 07:55 patients.csv
-rw-rw-rw- 1 lead    nurses   1830 Nov  9 08:02 shifts.txt

admin@clinic-fs:/srv/clinic$ chmod 754 report.txt
admin@clinic-fs:/srv/clinic$ ls -l report.txt
-rwxr-xr-- 1 lead nurses 2048 Nov  9 08:15 report.txt# the same result with the symbolic method:
admin@clinic-fs:/srv/clinic$ chmod u=rwx,g=rx,o=r report.txt

Tasks

1. shifts.txt (owner lead, group nurses). The owner and the nurses group can read and edit the shift list; everyone else can only read it.

   Show the answer

   admin@clinic-fs:/srv/clinic$ chmod 664 shifts.txt
   admin@clinic-fs:/srv/clinic$ ls -l shifts.txt
   -rw-rw-r-- 1 lead nurses 1830 Nov  9 08:02 shifts.txt

   Owner rw- (6), group rw- (6), others r-- (4).

2. patients.csv (owner records, group doctors). The owner can read and edit; doctors can only read; everyone else has no access.

   Show the answer

   admin@clinic-fs:/srv/clinic$ chmod 640 patients.csv
   admin@clinic-fs:/srv/clinic$ ls -l patients.csv
   -rw-r----- 1 records doctors 48211 Nov  9 07:55 patients.csv

   Owner rw- (6), group r-- (4), others --- (0).

3. backup.sh (owner itadmin, group it). A script. The owner and the information technology (IT) group can read, edit and run it; everyone else has no access.

   Show the answer

   admin@clinic-fs:/srv/clinic$ chmod 770 backup.sh
   admin@clinic-fs:/srv/clinic$ ls -l backup.sh
   -rwxrwx--- 1 itadmin it 912 Nov  8 17:40 backup.sh

   Owner rwx (7), group rwx (7), others --- (0).

4. kiosk.sh (owner itadmin, group it). A script. The owner and the IT group have full access; everyone else can read and run it but not change it.

   Show the answer

   admin@clinic-fs:/srv/clinic$ chmod 775 kiosk.sh
   admin@clinic-fs:/srv/clinic$ ls -l kiosk.sh
   -rwxrwxr-x 1 itadmin it 604 Nov  8 17:41 kiosk.sh

   Owner rwx (7), group rwx (7), others r-x (5).

In ls -l output the first character is the file type (- for a file, d for a directory). A + at the end of the permissions means extra permissions are set; view them with getfacl.