Unix System Administration Pt 3 - Day 1

Goals

• take permissions to the next level
• use setuid and setgid permissions
• work with symlinks
• enable selected users to sudo
• become a cron poweruser
• write menus for users
• start measuring system metrics

take permissions to the next level

• review of normal file permissions
• review of normal directory permissions
  • r - search directory contents (ls with no details)
  • w - allows creation and deletion
  • x - allows users to work with files they know about, but disallows ls. Allows cd
  • r-x - allows ls -l. No file creation or deletion.
• special file permissions
  • s - setuid, setgid: run with group or owner perms rather than executor...
• special directory permissions
  • t - sticky bit allows deletion only on owned files (/tmp)
  • s - setguid on directory makes new files owned by dir's group

use setuid and setgid permissions

• find / -type f \( -perm -2000 -o -perm -4000 \) find setguid/setuid files

use symbolic links

• hard link - another name for a file (link to an inode). File is deleted when last hlink is gone...
• symlink - link to name of a file (link to a name). Symlink outlasts the file itself...
• ln -s /path/to/file /path/to/link

sudo p9-11

The user will be prompted for their pass and will be able to run the app as root for a limited amount of invocations (generally 1) or for a number of minutes (generally 5).
This behavior is controlled by a /etc/sudoers file.

Danger!

Do not allow sudo to shell scripts or any app that has a shell in it

become a cron poweruser

• crontab -e edit in place
• crontab -l > outfile.txt dump crontab to a file
• crontab infile.txt read crontab from a file

write menus for users

early system metrics

• users on the system
• load
• responsiveness
• diskspace
• memory

Homework

1. job control p295
2. nice, renice p289-91.
3. restricted shells p187-88
4. shell wrappers (no reading)

Remember, your login is based on your machine's hostname, not on any other number.
~/[initials] refers to the subdirectory under your homedir, named after your initials. Everything except for .dotfiles will be stored in your ~/[initials] directory.