Chapter 15 System Administration

1. Chapter 15 System Administration By C. Shing ITEC Dept Radford University

2. Objectives • Understand system administrator’s duty • Understand the system start up and shutdown procedures • Understand how to maintain file systems and user accounts • Understand how to install software and peripheral devices • Understand how to configure kernel • Understand how to manage system accounting and security

3. System Admin Duty • Boot up and shutdown systems • Maintain and back up system • Maintain user accounts and system accounting • Install system and application software • Install and configure peripheral and kernel • Maintain network interface and system security

4. System Admin Account • Root: user ID is 0 • Hard to correct problems if made mistake • Become superuser: use su utility to create a child shell of root • sudo: provide special privilege for a specific task

5. System Start up • Power up self test • Load kernel to RAM • Kernel start running and initialize itself • Kernel starts first process PID=1(init), then it spawns child processes (getty) for creating and maintaining login shell using /etc/inittab to decide runlevels • Run fsck to check file systems (use sync utility to fix damaged file systems) • Mount file systems use mount for entries in /etc/vfstab file • Start daemons

6. System Run Level (Mode) • BSD system in either of the 2 modes: • Single-user: create a Bourne shell • Only / is mounted automatically • Need manually mount other file systems for system repair, back-up, kernel reconfiguration • Multi-user • Start daemons by running boot up file /etc/rc • Start locally maintained services by running boot up file /etc/rc.local • Clear files in /tmp

7. System Run Level (Mode) (Cont.) • BSD system in either of the 2 modes: • Multi-user (Cont.) • Create getty processes for every terminal in /etc/ttytab file • Start up network services, default mode • Start login process by replacing getty process when detect login attempt • Start up shell replaces login shell for successful login • Store login username in /etc/utmp and login session in /var/adm/wtmp

8. System Run Level (Mode) (Cont.) • BSD system in either of the 2 modes: • Multi-user (Cont.) • Logout: init process receives SIGCHLD signal • remove username in /etc/utmp and logout session in /var/adm/wtmp • Create a new getty process for the freed terminal

9. System Run Level (Mode) (Cont.) • System V in either of the 8 levels: • 0-6: can have own boot-up script for each level • 0 : firmware • 1 or S: for Single-user mode • 2: muti-user, no network • 3: multi-user, network • 4: not used • 5: shutdown for power off • 6: reboot

10. System Run Level (Mode) (Cont.) • System V in either of the 8 levels: • Boot-up files are /etc/rc0, /etc/rc1,…, /etc/rc6, /etc/rcS • Run level scripts are in /etc/rc0.d, /etc/rc1.d, …, /etc/rc3.d, /etc/rcS.d • Start up script: name begins with S • Shutdown script: name begins with K • All process management scripts are in /etc/init.d directory

11. System Shutdown • shutdown –option time [message] • Option: h – halt r – reboot • Time: now – shutdown immediately +minutes – within minutes hours:minutes – within hours and minutes Example: shutdown –h now

12. System Shutdown (Cont.) • halt • reboot • sync update super-block

13. Maintain File System • fsck –p [filesystem] • Automatically correct inconsistency on filesystem • Free block also inode • Used block but not inode • More than 1 inodes reference 1 block • Wrong block number • Wrong inode link count • Inode not in any directory

14. Maintain File System (Cont.) • df -k [filesystem] • Report in 1K block the disk space used/available for the mounted filesystem Example: df -k

15. Maintain File System (Cont.) • du -option [filename] • Option: k – 1K block s – size only • Report in 1K block the disk usage for the filename recursively down to subdirectories Example: du –k .

16. Maintain File System (Cont.) • quota [-v] [username] • Display [username’s] disk quota Example: quota

17. Maintain File System (Cont.) • format [-d diskname] [-p partition] • Format partition on diskname • Disk partition rule: • Swap space: 2 to 2.5 * RAM size • Partitions needed: /, /usr, /var, /tmp, /export through NFS, /opt

18. Maintain File System (Cont.) • Red Hat server partition recommendation: (128 MB RAM) • /: 256 MB • Swap: 256 MB • /usr: 512 MB + • /boot: 16 MB • /home: user accounts: 512 MB + • /var: server log for a long time • /tmp or link to /var/tmp Note: combine partition space if not needed

19. Maintain File System (Cont.) • Red Hat client partition recommendation: (32 MB RAM) • Swap: 64 MB • /boot: 16 MB • /: rest

20. Maintain File System (Cont.) • Solaris server partition recommendation: (Dedicated server) • / • Swap • /usr: shared system files • /opt: larger for NFS service • /export • /export/home: holds user accounts • /export/swap: for serve diskless client • /var: server log for a long time • /tmp or link to /var/tmp Note: combine partition space if not needed

21. Maintain File System (Cont.) • Solaris client partition recommendation: • / • Swap • /usr • /opt: if local optional software used • /var: client log for a long time • /tmp: if user or application use this a lot • /home: if workstation contains user accounts Note: combine partition space if not needed

22. Maintain File System (Cont.) • mkfs newfilesystem [sectornumber] • Create a newfilesystem (with sectornumber sectors) • newfs newfilesystem devicetype • Invoke mkfs using sectornumber specified by the devicetype in /etc/device.tab

23. Manage User Accounts • Add user entry in /etc/shadow and /etc/passwd files • Use vipw command to edit • Change password using passwd command • Add group entry in /etc/group file • Create home directory for the user • Set up owner, group and directory permissions • Provide start up files • .login and .cshrc files for start-up tc shell

24. Install Software & Configure Kernel • Deposit/Download software in appropriate directory • Solaris: under / • /kernel: Unix kernel (e.g. /kernel/genunix has about 1.5 MB) • /bin, /usr/bin: Unix utilities, built-in commands • /sbin: system binaries • /dev: device files • /lib: essential libraries • /usr/lib: libraries for C, FORTRAN, … etc • /var/log: log files • /var/adm: admin log files

25. Install Software & Configure Kernel (Cont.) • Deposit/Download software in appropriate directory • Solaris: under / (Cont.) • /etc: admin files, start-up files, configuration files • /opt: optional system software • /proc: pseudo file systems, contains managing process information • User application: under /usr/local, often a mount point for other file systems • /usr/local/bin: local software binary

26. Install Software & Configure Kernel (Cont.) • Modify configuration file for your environment • Use config utility to recompile kernel and create makefile for the architecture if not provided • Run make utility to produce executable file for the software • Reboot the system

27. Install Software & Configure Kernel (Cont.) • Example: Install Kerberos 5 On Red Hat Linux • cd /usr/local/bin • mkdir kerberos; cd kerberos • Now, download Kerberos 5 from web • tar -xzf krb5-1.3.1.tar.gz This uncompress and untar the file • ./configure --without-krb4 This recompiles kernel and create a makefile to exclude Kerberos 4 support • make This compiles necessary system files for Kerberos 5 • make install This creates executables and puts them in the right directories

28. Install Peripheral Devices • Install device driver • Find major and minor number of the device • Associate the device with device driver • mknod devicename option majornumber minornumber • Option: b – block device c – character device

29. Install Peripheral Devices (Cont.) • Example: • mknod /dev/disk1 b 4 0 disk is a block device

30. Install Peripheral Devices (Cont.) • Terminal files: • /etc/termcap (/etc/terminfo): complete terminal information • /etc/ttydefs: define terminal baud rate

31. Manage Network Devices • ifconfig utility to configure network interface • Ifconfig interfacename ip-address netmask [up/down] assign ip-address to interfacename and running/shutdown • Route utility to manually manage routing table • route add/delete ip-address netmask gateway create/delete an entry to ip-address in the routing table

32. Manage Network Devices (Cont.) • netstat -r display routing table

33. Manage System Accounting and Security • acct • Display accounting information • System usages store in /etc/adm/acct directory, use sa utility • Login/logout information stored in /usr/adm/wtmp file, use ac and last utilities

34. Manage System Accounting and Security (Cont.) • Security • Disable unused ports • Disable commands/methods that avoid password • rlogin, rsh • Disable utilities with known security problem • ping, finger • Do not log on root account unless necessary • Logon your regular account and use su utility to get super-user privilege • Watch files with SUID and SGID set • /tmp has sticky bit set: only owner can modify or delete files • Use secure protocols • Use secure telnet to replace telnet

35. Misc. • uname –a Prints system information • dmesg Display system diagnostic information such as memory, devices

36. Reference • Ch. 15 • Ch. 2 & 3 of Nemeth etl.