Transcript cis52-Chap15

Chapter 15
System
Administration
© 2000-2002 John Urrutia. All rights reserved.
1
Chapter 15
(Topics)
Background
The System Administrator & SuperUser
Types of Files
Description of System Operations
Important Files & Directories
© 2000-2002 John Urrutia. All rights reserved.
2
Chapter 15
(Topics)
System Administration
Day-to-day
Periodic
Preventing & Fixing Problems
Useful Utilities
Getting Help
© 2000-2002 John Urrutia. All rights reserved.
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Background
Because of Linux’s flexibility to operate on
many platforms with a large diversity of
hardware this chapter offers an overview of
fundamentals that apply to all Linux Systems
We look at some tools used in administration
Kernel construction and re-configuration
Disaster Recovery
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The System Administrator
Responsible for:
The care and feeding of Linux.
Addition, Deletion and updates to all
system resources.
Disaster Recovery.
Users
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The System Administrator
root aka The SuperUser
Has total and complete access to all
system functions and data.
SuperUser Login from:
system console or any terminal by using
Substitute User (su) command
sudo allows specific command
privileges to normal users.
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The System Administrator
When you use su to login as root
generally your command line prompt will
show a pound sign (#) instead of a
dollar sign ($)
To return to a normal user type exit or
Ctrl+d
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The System Administrator
Most System Administration tools are
located in these directories
/sbin
/usr/sbin
When executing these tools specify the
absolute pathname! Don’t rely on the
$PATH because of security
considerations.
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Types of Files
Ordinary files contain all types of user
data
text, programs, scripts, etc.
Directory files contain information about
all files (as outlined on next slide)
Special files primarily for devices,
named pipes, and sockets
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Types of Files
Directory files contain information about all
files
Type, Permissions, Links, Owner, Group, Size,
Name
Date & Time of: - creation, update, access
Inode: internal number that the file is known as
to the system. Owner, size, where located, link
count & other attributes.
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Types of Files
Special files
By convention are stored in /dev directory and
represent devices.
Each device file is identified in the directory by a
type indicator:
 b – block
 c – character
 d – directory
 l – link
 p – named pipe
 s – socket
© 2000-2002 John Urrutia. All rights reserved.
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Types of Files
Special files
By convention are stored in /dev directory
and represent devices.
fifo special files (aka Named Pipes)
 first in first out
Allows any two processes to exchange info
and are treated just like files.
sockets – basis of networking facility
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Types of Files
Character and Block Special files
block and character devices fall into
categories identified by a device number
Major device number – Identify the category
of hardware represented by the device
Minor device number – Identify a specific
device of that category
Created by mknod
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Types of Files
Character and Block Special files
The standard block devices on a Linux
system are disk drives.
 Anything that is not a block device is
considered a character device.
Printers, terminal, keyboards, modems.
Data can be read:
 in raw mode one character at a time
 By the “line”
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System Operation
Description of operation
Booting the system
System operating modes
Logging In, Running and Logging Out
Bringing the system down
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System Operation
Booting the system
Process of initializing the hardware,
loading the operating system and allowing
users access in normal operation mode.
Power-up
Hardware self-checks
BIOS execution
Boot loader (lilo – linux loader)
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System Operation
Boot loader
(what St. Nicholas of Myra does)
Master Boot Record
First block(s) of data on the hardware
specified start-up disk.
lilo is the initial program used to locate, load,
and run the operating system kernel.
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System Operation
Boot loader (Continued)
Six phases to nirvana
Loading and initialize the kernel
Device detection and configuration
Creation of spontaneous system processes
Operator intervention (Manual Boot Only)
Execution of system startup scripts
Multi-user operations
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System Operation
System operating modes
System Halt
– run level 0
Single-User
– run level 1 - S
Multi-User
– run level 2 - 3
X-windows
– run level 5
Reboot
– run level 6
Undefined
– run level 4, 7 - 9
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System Operation
Single User Mode
This mode is generally used for
maintenance or problem solving.
During the boot process this mode is
used:
 To do file system integrity checks.
Start the init process and run inittab, rc.M
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System Operation
Multi User operations
Logging In
init spawns mingetty to capture the terminal
login and display the login message, mingetty
identifies the terminal type at login and
overlays itself with the login process,
validates password, initializes your
environment
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System Operation
Multi User operations
Running
Enter command or exit / logout
Logging Out
Kills your login shell process
init receives the signal and cleans-up
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System Operation
Bringing the system down
shutdown brings the system down in an
orderly fashion. And it can:
Change the mode of system operation.
Schedule the time to shutdown
Warns users before shutdown
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System Operation
Normal shutdown does the following
wall – warns users to logout
/etc/nologin created to prevent new logins
kill – issued for all processes
sync; sync – finish writing buffers
umount -a – dismount all filesystems
telinit -s – set single user mode
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System Operation
Abnormal shutdown or crashes
System halts without cleanup
Status of system is unpredictable
May have one or more core dumps
System must be restarted with caution
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System Operation
System re-start after a crash
fsck utiltity checks and repairs the following
errors:
 Inodes, blocks, and sizes
 Directory structure
 Directory connectivity
 Reference counts
Note: filesystems must not be mounted
or mounted as readonly
If file integrity is okay – normal startup will
follow
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System Operation
If errors are detected and fixed
Notify file users to beware of missing or
inaccurate data.
Restore files from backups
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Important Files & Directories
/dev/null – the bit bucket
/var – frequently changed system files
System logs
/var/spool/cron – controls what interval
jobs are executed.
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Important Files & Directories
/etc/group – contains the user groups
allowing members to share data files.
newgrp – spawns shell under new group
id – will show uid, current gid and groups
/etc/mtab – list of all mounted devices
Controlled by mount and umount utility
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Important Files & Directories
/etc/passwd – identifies system users
login-name: – your login id (ie. jurrutia)
password: – the encrypted password
user id number: – the internal UID
group id number: – the default GID
comment: – whatever you want
directory: – absolute pathname to home
program – default login program to run (bash)
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Important Files & Directories
/etc/passwd – example
root:x:0:0:Root of all:/:/bin/sh
mpress:x:521:0:M Press:/home/mpress:/bin/bash
who:x:1000:1000:Ex who & leave:/usr:/usr/bin/who
/etc/profile – the shell login script
First script your shell runs after login
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Important Files & Directories
/etc/shadow – stores encrypted passwords and
other user info. Only accessible by root.
login-name: – your login id (ie. jurrutia)
password: – the encrypted password
last modified: – modification date (days since 1/1/70)
min: – min. # of day before password can be changed
max: – max. # of day before password must change
warn: – days to warn of password expiration
inactive: – set acct. inactive after password expires
expire: – days since 1/1/70 when acct will expire
flag: – reserved for future use
© 2000-2002 John Urrutia. All rights reserved.
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Important Files & Directories
Don’t try (modifying) this at home!
/etc/shadow – is modified by:
passwd – change password
useradd – add a new user
usermod – change existing user
userdel – delete a user
© 2000-2002 John Urrutia. All rights reserved.
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Important Files & Directories
/etc/fstab – file system table identifies all
the file systems available to the system. It
contains 6 fields (white space delimited):
Block device name
Mount point
Filesystem or device type
Mounting option
Filesystem backup (when to run dump utility)
fsck order to check
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Important Files & Directories
#Device
Mountpoint
FS Type Options
Dump Pass#
LABEL=/
/
ext3
defaults
1
1
LABEL=/boot /boot
ext3
defaults
1
2
LABEL=/home /home
ext3
defaults
1
1
/dev/fd0
/mnt/floppy auto
noauto,owner
0
0
none
/proc
proc
defaults
0
0
none
/dev/shm
tmpfs
defaults
0
0
none
/dev/pts
devpts
gid=5,mode=620
0
0
/dev/hda6
swap
swap
defaults
0
0
/dev/cdrom
/mnt/cdrom
iso9660 noauto,owner,kudzu,ro
0
0
/home/SWAP
swap
swap
0
0
defaults
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Important Files & Directories
/vmlinuz – The LINUX system kernel
The z indicates the kernel is in a
compressed format. Generally the last
character is x .
/sbin/shutdown – Shutdown Program
 Program to bring the system down
© 2000-2002 John Urrutia. All rights reserved.
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System Administration (Day to Day)
Backing Up Files – why bother
System malfunctions User indiscriminate deletions –
What to consider
How much work are you willing to lose?
How often are you willing to back-up files?
Time, storage media
Partial vs full backups
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System Administration (Day to Day)
What to use for backups
Type
Speed
Capacity
Cost
Slow
High
Low
CD-ROM,RW
Medium
Medium
Medium
Hard Drives
Fast
Medium
High
Removable
Medium
Low
Low
Tape
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System Administration (Day to Day)
Programs to use for backups
tar – tape archive utility
cpio – copy in and Out directory trees to
archive (antiquated)
afio – Copy and restore directory trees to
archival files
taper – A user friendly backup and restore
utility
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System Administration (Day to Day)
tar – tape archive utility
Create an archive file
Add to an archive file
List archive file
Retrieve from archive file
tar option [modifiers] [file-list]
--create
--append
--list
--
--extract
--get
--update
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System Administration (Day to Day)
tar option [modifiers] [file-list]
--absolute-paths
--exclude filename
--file filename
--verbose
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System Administration (Day to Day)
crontab – Creates a list of scheduled tasks
The cron table created contains 6 fields
 Minutes
 0 thru 59
 Hours
 0 thru 23
 Day of Month
 1 thru 31
 Month of year
 1 thru 12
 Day of week
 0 thru 6
The values can be
combinations of absolutes
and ranges. Each field is
IFS delimited.
All cron files are stored in the
/var/spool/cron/crontabs
Directory.
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System Administration
Periodic
Installing LINUX
Floppy
CD-ROM
Rescue Disks
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System Administration
Re-building the kernel
make config
make dep; make clean
make zlilo
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Preventing & Fixing Problems
When a User Cannot Log In
useradd
userdel
Usermod
Suspect files
/etc/passwd
.profile – .login – .bashrc
/etc/inittab
© 2000-2002 John Urrutia. All rights reserved.
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Preventing & Fixing Problems
System logs
/var/log
Track various events in system
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Useful Utilities
Simple commands
du – disk usage
df – display filesystems
chsh – change your shell
mount – attaches a device to the system
Relies on the etc/fstab file for information
about the device to mount
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Useful Utilities
mount –t msdos /dev/fd0 /mnt
Mounts the floppy drive as a MSDOS
device with its root at the /mnt directory
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Getting Help
man pages
Info pages
© 2000-2002 John Urrutia. All rights reserved.
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