chapter_6
DESCRIPTION
ccTRANSCRIPT
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TROUBLESHOOT LINUX
SYSTEM CHAPTER 6
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TROUBLESHOOT METHODOLOGY
The maintenance cycle
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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
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Documentation: System information stored in a
log book for future references
Troubleshooting procedures: Tasks performed
when solving system problems
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Common troubleshooting procedures
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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
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Two categories of problems:
Hardware-related
Software-related
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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
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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
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The kudzu welcome screen
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Configuring new hardware using kudzu
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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
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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.
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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
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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
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/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
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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
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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
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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
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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
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Lost root password
First, you have to reboot into recovery mode.
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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.
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From the boot menu, select recovery mode, which is
usually the second boot option.
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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.
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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
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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
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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.
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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!
exit