Chapter 15 System Administration

By C. Shing

ITEC Dept

Radford University

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

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

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

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

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

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

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

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

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

System Shutdown

• shutdown –option time [message]– Option: h – halt

r – reboot– Time: now – shutdown immediately

+minutes – within minuteshours:minutes – within hours and

minutes

Example:shutdown –h now

System Shutdown (Cont.)

• halt

• reboot

• sync

update super-block

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

Maintain File System (Cont.)

• df -k [filesystem]– Report in 1K block the disk space

used/available for the mounted filesystem

Example:

df -k

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 .

Maintain File System (Cont.)

• quota [-v] [username]– Display [username’s] disk quota

Example:

quota

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

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

Maintain File System (Cont.)

• Red Hat client partition recommendation: (32 MB RAM)– Swap: 64 MB– /boot: 16 MB– /: rest

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

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

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

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

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

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

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

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

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

Install Peripheral Devices (Cont.)

• Example:– mknod /dev/disk1 b 4 0

disk is a block device

Install Peripheral Devices (Cont.)

• Terminal files:– /etc/termcap (/etc/terminfo): complete terminal

information– /etc/ttydefs: define terminal baud rate

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

Manage Network Devices (Cont.)

• netstat -r display routing table

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

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

Misc.

• uname –a

Prints system information

• dmesg

Display system diagnostic information such as memory, devices

Reference

• Ch. 15

• Ch. 2 & 3 of Nemeth etl.