How to Administer Linux: The Basics

Last updated: 20 Oct 2014

Overview

Overview of Linux and system administration; hands-on experience with basic administration tasks; testing results

Workshop Duration

2 hrs.

Student Prerequisites

use of Unix/Linux

Student Provides

nothing

Lab Provides

computer with Linux installed
itadmin and ituser accounts and passwords

Preparation

Fresh installation of Fedora to x cloned disks
Disk drives inserted and locked into computers
Setup root account with password

Delivery

What is System Administration?
1. Defining system
2. Adding/removing/updating hardware and software
3. Configuring hardware, software, file systems, etc.
4. Ensuring data integrity
5. Managing user accounts/helping users
6. Managing resources
7. Handling problems
8. Monitoring operation
  - Security
  - Performance
  - Functionality
9. Interfacing with other systems
10. Defining and enforcing policies
Basic vs. Advanced Administration
1. Basic
  1. single user
  2. sharing/fairness not an issue
  3. downtime is acceptable (no 24x7 requirement)
  4. no limits
  5. no policy
2. Advanced
Focus of Workshop
1. Understand Linux design and operation
2. Emphasize commands vs. GUI
3. Expose simple monitoring tools
4. Encourage backup/restore
5. Maybe mention interfacing
6. Provide hands-on time
How Linux Starts
1. BIOS
2. boot from device
3. decompress RAM image into RAM
4. run RAM image
5. detect rest of hardware
6. mount device as root (/)
  - IDE and CD/DVD: /dev/hd[a-z][1-9]
  - SCSI/SAS/SATA/USB: /dev/sd[a-z][1-9]
  - could be on CD/DVD/USB
7. transfer control from RAM to root
8. start init process then startup scripts
9. single vs. multi-user?
From where?
1. /boot -- RAM image, kernel
2. / (root)
3. /etc/sysconfig and /dev
4. PATH=/bin:/sbin:/usr/bin:/usr/sbin
5. /etc/rc.d and /etc/init.d
  startup and shutdown scripts, in order
6. /lib; /proc; /tmp; /var; /opt; /home; /usr; /mnt
File system (fs)
1. File types: regular/dir/char & block devices/sockets/pipes/links/sh mem
2. absolute vs. relative paths
3. file redirection
```
    0 is stdin: <filename
    1 is stdout: >filename (or >> to append)
    2 is stderr: 2>filename (common: 2>&1 -- put same place as stdout)
    
```
4. file attributes
  1. owner and group (chown, chgrp)
  2. permissions (chmod, umask)
    See via:
```
      > ls -l
      -rwxr--r--  1 labadmin labadmin      267 Nov  6  2006 fix_perms
      
```
    - symbolic type: ugo
    - symbolic permissions: rwx
    - can also use octal
    - umask is 777-perms
5. make a fs on a device
  See via:
```
      > df -h
      
```
  - partition or Logical Volume Manager (LVM)
    simplicity vs. expandability
  - partition: MAKEDEV, then fdisk or other partition tool
```
        > fdisk /dev/sda
        
```
  - put a file system on a partition
```
        > mkfs -t ext4 /dev/sdb3 (for example)
        
```
    fsck for large disks takes a long time. Using a journaled file system (e.g., ext3, ext4) is much quicker.
6. mount device to a directory (usually empty)
  If you don't want to mount manually, put the mount info in the /etc/fstab and it will attach at startup or when requested.
  - umount device or directory to unmount
    device must not be in use, or it will fail. To see who is using a device, use fuser command
  - CDs and DVDs can be mounted (may need "-t iso9660")
  - floppy (/dev/fd0 is device; "-t msdos" is type of FS)
  - file system (e.g., "-t nfs", "-t msdos", "-t samba")
  - entries stored in /etc/mtab
Users and groups
1. User directory: /etc/passwd
  - useradd, usermod, userdel
  - /etc/shadow is secure version with passwords
  - run pwconv if edited /etc/passwd drectly
  - for service accounts, use "/bin/nologin" as default
2. /etc/group
  - groupadd, groupmod, groupdel
  - grpconv may be neceesary
3. /etc/skel and /etc/profile.d
Processes
1. init is pid 1; mother of all processes
  - config file: /etc/inittab
  - parent of all
  - spawns getty which starts "login"
2. fork clones a process; everything except id
  environment variables, standard file descriptors, memory map of code
3. exec substitutes current code for new code, and may change environment
4. list processes: ps aux
5. monitor processes: top
6. kill process: kill -KILL pid
7. use nice to start, or renice to change a command's resource usage
Brief word about Terminals
1. console: login; messages are written here
2. terminals (tty), pseudo-terminals (pty, pts)
3. serial communications; modems work this way
Daemons/services
1. on from startup to shutdown
2. scripts to control in /etc/init.d
  This is the old style. New services are controlled by systemctl.
3. service control
  - old way
```
       service ___ start/stop/restart/status
       
```
    For example:
```
       service network restart
       
```
  - new way
```
       systemctl start/stop/restart/status ____
       
```
    For example:
```
       systemctl start network
       
```
4. modifying service for startup
  - old way
    - chkconfig --list ___
    - chkconfig ___ on
    - chkconfig ___ off
  - new way
    - systemctl status ____
    - systemctl enable ____
    - systemctl disable ___
5. services often create log files
6. services should be associated with non-root service account
7. config files often in /etc/___.conf
8. superserver: /etc/xinetd.d
Desktop
All X Window System based, allowing remote display of GUI (keyboard, mouse, display, window movement).
1. Gnome/KDE/etc.
2. switch to console mode: Ctrl-Alt-F1..F6
3. switch to desktop mode: Ctrl-Alt-F7
4. some admin tasks easier through GUI
Tasks
1. searching files
```
    grep root /etc/passwd
    
```
2. backup
  Can also send backups over net.
  - tar -zpscf full_backup.tar /
  - dump -0 -f full_backup.dmp -b 64 -z3 /dev/VolGroup00/LogVol00
3. restore
  Can also restore files from net.
  - cd /tmp && tar -zxf full_backup.tar
  - restore -r -b 64 -f full_backup.dmp
4. periodic processes (cron)
  - per user: crontab -e
    might have to set EDITOR environment variable
  - /etc/cron.hourly;/etc/cron.daily;/etc/cron.weekly;/etc/cron.monthly
  - /etc/cron.d
5. logs
  - /var/log/messages;/var/log/dmesg
  - config logging: /etc/syslogd.conf
  - rotate logs to avoid overfilling /var: /etc/logrotate.conf;/etc/logrotate.conf
6. finding files
  - find . -name ___ -print
  - locate ___
    requires onetime ("updatedb") or periodic process to update the database of files (/etc/cron.daily/mlocate.cron)
7. help
  - man ____
  - info ____
8. command searching
  - which ____
    finds which command in the PATH
  - echo $PATH
    shows path
  - export PATH=$PATH:____
9. networking information
  - network interface definitions
    - old way: /etc/sysconfig/network-scripts/ifcfg-xxxx
    - new way: /etc/NetworkManager/NetworkManager.conf
  - display network interface information
    - old way: ifconfig
    - new way: ip addr show
Hands on time
1. Create ituser2 account with wheel group membership and give it a password
  From command line:
```
    useradd -d /home/ituser2 -m -G wheel -c "IT User 2" ituser2
    passwd ituser2
    id ituser2
    
```
2. Create ituser3 account with standard user group membership and give it a password
  Use the GUI.
3. Create a "demo" group, and add ituser2 and ituser3 to it.
```
    groupadd demo
    usermod -a -G demo ituser2
    id ituser2
    usermod -a -G demo ituser3
    id ituser3
    
```
4. Login as ituser2
  Switch from GUI to console: Ctrl-Alt-F4
5. elevate privileges
```
    sudo bash
    
```
  Note the difference between standard user and this. Try the same with ituser3 — what happened and what is the difference?
6. Create a ~/test directory and a put a file in it
  Tilde ("~") in a bash shell means use the current home directory.
  1. mkdir ~/test
  2. echo hi >~/test/textfile
  3. mkdir ~/test/subdirectory
7. Backup/restore
  1. Backup every detail about files
```
      tar zpscvf backup.tgz test
      
```
    Look at contents of the archive:
```
      tar ztvf backup.tgz
      
```
  2. Delete test subdirectory
```
      rm -ri ~/test
      
```
    Note the danger of rm -rf.
  3. Restore the deleted files
```
      cd /tmp
      tar zxvf ~/backup.tgz
      
```
    Move restored files and directories to correct directory.
8. Change permissions on ~/test while logged on as ituser2
  1. Give world read to ~/test
```
      chmod o+r ~/test
      ls -ld ~/test
      
```
  2. Change ownership of ~/test to allow demo group access.
```
      chgrp demo ~/test
      ls -ld ~/test
      
```
  3. Set read and execute on ~/test/textfile for ituser ONLY
```
      chmod u=rx,g-rwx,o-rwx ~/test/textfile
      
```
  4. Use su with ituser3 to determine if ituser3 can read "/home/ituser/test"
```
      su ituser3
      ls -l /home/ituser/test
      exit
      
```
9. Run top
  1. Explain fields, use O command to change sort order
  2. Which task uses the most CPU?
  3. Which task uses the most memory?
10. Create a task to write to a log file every 5 minutes.
```
    crontab -e
    # add this line:
    5 * * * * echo 5 minutes passed >/home/ituser/mylog
    # save the file
    
```
11. Enabling and disabling system daemons
  1. Stop sendmail
```
     service sendmail stop
     
```
  2. Look at /var/log/messages
    Very useful to look only at the end of it:
```
     tail /var/log/messages
     
```
  3. Use chkconfig to turn off sendmail permanently
```
     chkconfig sendmail off
     chkconfig --list sendmail
     
```
12. Firewalling
  1. firewall editing
    - old way: iptables, gui editing, command line editing and web resources.
    - old way: firewalld, gui editing, command line editing and web resources.
  2. Block pings
  3. log dropped packets
  4. ping localhost
Useful urls for assisting with administration tasks:
1. http://tldp.org/
  A document repository for everything linux

Cleanup

Clone the disk drives