1. Users/Groups/Permissions

2. Homework/Lab Issues
Lab 1: 8, 11h
Homework 2: 1

3. /etc/[passwd|shadow] format
passwd-> sj86672:x:28856:1000:Stuart A Jaskowiak(Blue Ash):/home/sj86672:/bin/ksh
shadow-> sj86672:$1$iOk/Ynmi$FIfiuUKYy9K3DuUCr1qmX0 :14122:0:99999:7:::
x in column 2 means /etc/shadow has to exist
UIDs (column 3) should be unique, but don't have to be
/etc/shadow stores password specific info

4. Groups Linux uses a private group by default sj86672:x:1000:
adm:x:4:sj86672
dialout:x:20:sj86672

5. Tools to maintain users/groups
GUI - “System”, “Administration”, “User and Groups”
Command Line
useradd, usermod, userdel
groupadd, groupmod, groupdel
vipw, vigr (dangerous)

6. Permissions 3 categories: drwxrwxr-x User (people with same UID)
Group (people with same GID)
Other (people with neither)
r = 4
w = 2
x = 1

7. Ways to Change Permissions
chmod u+rwx,g-rwx,o-rwx my_file
chmod 700 my_file

8. Misc Commands su – switch user passwd – change passwords
With a – and without a - are not 100% identical
passwd – change passwords
chage – check on password aging

9. Useful Links
admin-made-easy/shadow-file- formats.html

10. Permissions, Links and the File System

11. Permissions
3 categories:
drwxrwxr-x
User
Group
Other

12. Ways to Change Permissions
Start perms:
chmod u=rwx,g=,o= my_file
chmod u+rwx my_file
chmod 700 my_file
End perms: -rwx------
r == 4
w == 2
x == 1

13. Symbolic Links Shortcut to another file (like windows shortcut)
~/cit370
$ ls -l
total 1
-rwx sj86672 staff 0 Oct 5 15:09 my_file*
lrwxrwxrwx 1 sj86672 staff 7 Oct 5 15:14 other_file -> my_file*

14. Sym link permissions Controlled by originating file not link
Sym link perms: lrwxrwxrwx
chmod actually changes permission on linked file!

15. Display filesystem info
df – displays information about disk layout and usage
~]# df
Filesystem K-blocks Used Available Use% Mounted on
/dev/sda % /
/dev/sda % /var
/dev/sda % /opt
/dev/sda % /boot
tmpfs % /dev/shm

16. Umount error [15:18:48]root@wiley ~ # umount /var umount: /var busy
Open file someplace in /var

17. du Show space used by individual files Default only shows directories
du -a shows files

18. File Types Symbol Meaning - Regular File d Directory l Symbolic Link b
Block Special File c
Character Special File s
Socket p
Named Pipe

19. find Allows you to find a file in the file system structure
find ~ -name “*txt” –ls
find /etc –name “*cons*” -ls

20. find arguments mtime – last modified time +1 = more than one day ago
-1 = less than one day ago
size – size of file
#[cwbkMG]
type – type of file (see file types slide)
ls – long listing, equivalent to ls -dils on each file