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Linux+ Study Guide (XK0-002)
Troubleshooting
In order to make
troubleshooting as easy as possible, you should always use an
organized methodology. Using simple best practices will do just
that.
Best practices
The best tip when it comes to troubleshooting best practices is to
document all of your operations. This will prove helpful in critical
situation as you will be able to find out about service
dependencies, permission issues, etc. Start with quick fixes: if a
problem sounds familiar, try using a couple of quick tricks. This
often addresses the issue. Do not act randomly: use a proper order
to find a problem. E.g. beginning by looking at hardware, then
software, looking at recent changes, looking at logs, asking the
user about the nature of the problem (sometimes the problem can be
the user), etc. If all symptoms seem to point at a certain service
or process, you can kill and restart it.
You are expected to be able to inspect and determine cause of errors
from system log files using such commands as locate, find, grep, ? ,
<, >, >>, cat, tail.
A lot of error messages in linux come from different versions of
software and the dependencies associated with them. If you change or
update a php package for example, a php based program might stop
working. You should use the rpm command to
view proper dependencies, document any changes and verify
dependencies before making any changes.
Troubleshooting the file system
To verify and repair a file system, you can use the
mount command to enumerate the different
partitions on the system and the fsck command
to repair them.
You can use the DF command to see the space used on each disk.
Problems can occur when a disk is full.
Troubleshooting the boot process
Even with the strongest file systems, failure will happen. You may
encounter situations where the system boots in single user mode.
This is an operating mode that doesn’t start all daemons and is
useful for troubleshooting. In this mode you will be given the
opportunity to use different troubleshooting tools including file
system integrity using fsck. In the case
where a system won't boot, it is a good idea to boot from a floppy
and inspect the filesystem and boot sector. A boot disk should
always contain fsck as it will enable you to repair and rescue a
damaged file system.
Troubleshooting backup and restore errors
Backups can fail for many reasons. The most common causes are media
and drive related issues. Most media requires proper maintenance and
cleaning. Tape corruption, low device space or write failures are
common problems. Proprietary software will have specific error
messages and you should refer to your software provider to verify
them. Backups should always be handled with care. You should do a
regular restore test as it is not uncommon to see successful backups
that cannot be successfully restored.
Troubleshooting Networking
Linux, being based on one of the oldest network operating systems
(UNIX), is loaded with standard troubleshooting tools. Some of these
tools are:
Ping: the ping utility enables you to verify basic connectivity between two machines.
Route: the route utility helps you take a look at the various routes defined within the Kernels routing table. You will be able to add, delete, and modify routing information here. This is very helpful when using your Linux box as a router or firewall.
Traceroute: this utility enables you to see every router between your Linux machine and a given host. This way it is possible to see any failing point between you and this host.
Netstat: this utility helps you see your network interfaces statistics.
Lsof: this utility lets you see any open files.
Ifconfig: this utility lets you see your network interfaces and modify certain settings.
Finding Help
Linux has one of the largest communities when it comes to finding
friendly support. Linux has specific terms when it comes to help. Here
are a couple:
- LUG: (Linux User Group) LUGs are friendly groups of users and exist in most large cities around the world. Lugs are a great way to have person to person support. You can find most Lugs at the following URL http://lugww.counter.li.org
- Howto: A howto is a detailed procedure for a specific topic regarding Linux. You can find a howto to help you implement just about any Linux software or Linux service. A great site about those can be found at http://www.tldp.org.
- Infopages: Those are really popular in northern Europe and they are filled with useful information. The hard part is finding one in English!
- ManPages: Although manpages are available in the shell, you are likely to find updated versions of them all around the Web.
- NHF: Newbie Help Files. NHF’s are an initiative of justlinux.com (previously linuxnewbie.org). They are easy to understand tutorials that will help new users understand the nuts and bolts about specific linux topics. You will find NHF’s at http://www.justlinux.com/nhf/.