TROUBLESHOOT LINUX

SYSTEM CHAPTER 6

TROUBLESHOOT METHODOLOGY

The maintenance cycle

Monitoring: Observing system areas for

problems or irregularities

Proactive maintenance: Minimizing

chance of future problems

e.g., perform regular system backups

Reactive maintenance: Correcting

problems when they arise

Documenting solutions

Developing better proactive maintenance

methods

Documentation: System information stored in a

log book for future references

Troubleshooting procedures: Tasks performed

when solving system problems

Common troubleshooting procedures

Two troubleshooting golden rules:

Prioritize problems according to severity

Spend reasonable amount of time on each problem given its

priority

Try to solve root of problem Avoid missing underlying cause

Justify why a certain solution is successful

Two categories of problems:

Hardware-related

Software-related

HARDWARE-RELATED PROBLEMS

Hardware-Related Problems

Often involve improper hardware or software configuration

SCSI termination

Video card and monitor configuration

POST test alerts Loose hardware connections

IRQ or I/O address conflicts View output of dmesg (control or print the kernel ring

buffer) command

Absence of device drivers prevent OS from using

associated devices

Kudzu program: Detect and install support for

new hardware

If hardware device not detected, device driver must

be configured manually

HDDs most common device to fail

Good idea to use RAID

The kudzu welcome screen

Configuring new hardware using kudzu

If HDD containing partitions mounted on noncritical directories fails:

Power down computer and replace failed HDD

Boot Linux system

Use fdisk to create partitions on replaced HDD

Use mkfs to create filesystems

Restore original data

Ensure /etc/fstab has appropriate entries to mount filesystems

If HDD containing / filesystem fails:

Power down computer and replace failed HDD

Reinstall Linux on new HDD

Restore original configuration and data files

You should update your package every time you made changes to your system

(hardware/software).

You can run PUP, yum, apt-get, or GUI based synaptic package manager to do

the update.

SOFTWARE-RELATED PROBLEMS:

APPLICATION-RELATED PROBLEMS

Missing program libraries/files, process restrictions, or

conflicting applications

Dependencies: Prerequisite shared libraries or

packages required for program execution

Programs usually check at installation

Package files may be removed accidentally

rpm V command: Identify missing files in a package or package dependency

ldd command: Display shared libraries used by a program

ldconfig command: Updates /etc/ld.so.conf and /etc/ld.so.cache files

/etc/ld.so.conf file: List of directories containing shared libraries

/etc/ld.so.cache file: Contains location of shared library files

compressor/decompressor (codec) file: Contains rules to compress or decompress multimedia information

ulimit command: Modify process limit

parameters in current shell

Can also modify max number of filehandles

/var/log directory: Contains most system log files

If applications stop functioning due to difficulty

gaining resources, restart using SIGHUP /

SIGHKILL

SOFTWARE-RELATED PROBLEMS:

OPERATING SYSTEM-RELATED PROBLEMS

Most software-related problems related to

OS

Boot loader, filesystem, serial device problems

LILO problems: Place linear in, remove compact from /etc/lilo.conf file

GRUB problems: Typically result of

missing files in /boot directory

mkbootdisk command: Create a boot

floppy diskette

If filesystem on partition mounted to noncritical

directory becomes corrupted:

Unmount filesystem

Run fsck command with f (full) option

If fsck command cannot repair filesystem, use mkfs

command to re-create the filesystem

Restore filesystems original data

If / filesystem is corrupted:

Boot from first Red Hat Fedora installation CD

Type linux rescue at welcome screen

Enter shell for Linux system on CD

Create new / filesystem via mkfs command

Restore original data to re-created / filesystem

Reboot system

Lost root password

First, you have to reboot into recovery mode.

If you have a single-boot (Ubuntu is the only operating system on your computer), you may have to press the Escape key during bootup in order to see the boot menu.

If you have a dual-boot (Ubuntu is installed next to Windows, another Linux operating system, or Mac OS X; and you choose at boot time which operating system to boot into), the boot menu should appear without the need to press the Escape key.

From the boot menu, select recovery mode, which is

usually the second boot option.

After you select recovery mode and wait for all the boot-up

processes to finish, you'll be presented with a few options. In

this case, you want the Drop to root shell prompt option so

press the Down arrow to get to that option, and then press

Enter to select it.

The root account is the ultimate administrator and can

do anything to the Ubuntu installation (including

erase it), so please be careful with what commands you

enter in the root terminal.

Once you're at the root shell prompt, if you have

forgotten your username as well, type

ls /home

You should then see a list of the users on your

Ubuntu installation.

To reset the password, type

username is the username you want to reset.

passwd username

You'll then be prompted for a new password. When you

type the password you will get no visual response

acknowledging your typing. Your password is still

being accepted.

Just type the password and hit Enter when you're

done. You'll be prompted to retype the password. Do so

and hit Enter again.

Now the password should be reset. Type to return to the recovery menu.

After you get back to the recovery menu, select resume normal boot, and use Ubuntu as you normally wouldonly this time, you actually know the password!

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