RHCSA: Finding Help

In normal environment Internet is the best medium for finding help. It contains man pages too. In exam environment only man pages and ISO are available. that mena that you need to study them and compare content of man pages with the books you study for exam. If examples are available you should try them just to better remember them. In other words the level of jnoledge of the contnet of man pages correpated with your chances to pass the exam.

Some manpages are convoluted (LVM,grub) and split on dozens of pages descbring individual utilities.

pvchange

Change attributes of a Physical Volume.

pvck

Check Physical Volume metadata.

pvcreate

Initialize a disk or partition for use by LVM.

pvdisplay

Display attributes of a Physical Volume.

pvmove

Move Physical Extents.

pvremove

Remove a Physical Volume.

pvresize

Resize a disk or partition in use by LVM2.

pvs

Report information about Physical Volumes.

pvscan

Scan all disks for Physical Volumes.

vgcfgbackup

Backup Volume Group descriptor area.

vgcfgrestore

Restore Volume Group descriptor area.

vgchange

Change attributes of a Volume Group.

vgck

Check Volume Group metadata.

vgconvert

Convert Volume Group metadata format.

vgcreate

Create a Volume Group.

vgdisplay

Display attributes of Volume Groups.

vgexport

Make volume Groups unknown to the system.

vgextend

Add Physical Volumes to a Volume Group.

vgimport

Make exported Volume Groups known to the system.

vgimportclone

Import and rename duplicated Volume Group (e.g. a hardware snapshot).

vgmerge

Merge two Volume Groups.

vgmknodes

Recreate Volume Group directory and Logical Volume special files

vgreduce

Reduce a Volume Group by removing one or more Physical Volumes.

vgremove

Remove a Volume Group.

vgrename

Rename a Volume Group.

vgs

Report information about Volume Groups.

vgscan

Scan all disks for Volume Groups and rebuild caches.

vgsplit

Split a Volume Group into two, moving any logical volumes from one Volume Group to another by moving entire Physical Volumes.

lvchange

Change attributes of a Logical Volume.

lvconvert

Convert a Logical Volume from linear to mirror or snapshot.

lvcreate

Create a Logical Volume in an existing Volume Group.

lvdisplay

Display attributes of a Logical Volume.

lvextend

Extend the size of a Logical Volume.

lvmconfig

Display the configuration information after loading lvm.conf(5) and any other configuration files.

lvmdiskscan

Scan for all devices visible to LVM2.

lvmdump

Create lvm2 information dumps for diagnostic purposes.

lvreduce

Reduce the size of a Logical Volume.

lvremove

Remove a Logical Volume.

lvrename

Rename a Logical Volume.

lvresize

Resize a Logical Volume.

lvs

Report information about Logical Volumes.

lvscan

Scan (all disks) for Logical Volumes

Some do not produce all the necessary information (yum, grub). Just try to get information about rb.break usage dring boot (root password recovery procedure):

On an average Linux system there are hundreds of commands are available each with dozens of options (way too many to ever be able to remember all of them). The most basic help system is man pages. During self-study it make sense to use Web version of man pages are they are cross-referenced with links.

Using man

When using the Linux command line, you will at some point consult man pages. Man is what makes working from the command line doable. If you do not know how a command is used, the man page of that command will provide valuable insight. This section covers a few man essentials.

To start with, the most important parts of the man page in general are at the bottom of the man page. Here you’ll find two important sections: In many cases there are examples; if there are no examples, there is always a “see also” section. This brings you to related man pages, which is useful if you have just not hit the right man page. To get to the bottom of the man page as fast as possible, use the G command.

To find information in man pages, you can search the mandb database by using the commands apropos or man -k. If the database is current, getting access to the information you need is easy. Just type man -k, followed by the keyword you want to search for. This command looks in the summary of all man pages that are stored in the mandb database. For example:

Based on the information that man -k is giving you, you can probably identify the man page that you need to accomplish whatever you want to accomplish. Be aware, however, that man -k is not perfect; it searches only the short summary of each command that is installed. If your keyword is not in the summary, you’ll find nothing and get a “nothing appropriate” error message.

While using man -k to find specific information from the man pages, you’ll sometimes really get a lot of information. If that happens, it might help to filter down the results a bit by using the grep command. But if you want to do that, it is important that you know what you are looking for.

Man pages are categorized in different sections. The most relevant sections for system administrators are as follows:

There are also sections that provide in-depth detail, such as the sections about system calls and library calls. When using man -k, you’ll get results from all of these sections. To limit the results that display, it makes sense to use grep to show only those sections that are relevant for what you need. So, if you are looking for the configuration file that has something to do with passwords, use man -k password | grep 5, or if you are looking for the command that an administrator would use to create partitions, use man -k partition | grep 8.

Another useful man option is -f. The command man -f <somecommand> displays a short description of the item as found in the man database. This may help you when deciding whether this man page contains the information you are looking for.

Updating mandb

When using the man -k command, the mandb database is consulted. It can sometimes happen that you are looking for something that should obviously be documented but you cannot find anything anyway and all you get is “nothing appropriate.” If that happens, you might need to update the man database. Doing that is easy: Just run the mandb command as root without any arguments. It will see whether new man pages have been installed and update the man database accordingly.

Tip: Do not try to memorize all the commands that you need to accomplish specific tasks. Instead, memorize how to find these commands and which man page to read to get more information about the command.

Let’s assume that you are looking for a command, using man -k, but all you get is a message “nothing appropriate” and you do not remember how to fix it.

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