Linux Shortcuts
and Commands:
Linux Newbie
Administrator Guide
by Stan and Peter Klimas
This is a practical selection of the commands we use most often. Press
<Tab>
to see the listing of all available command (on your PATH). On my small
home system, it says there are 2595 executables on my PATH. Many
of these “commands” can be accessed from your favourite GUI front-end (probably
KDE or Gnome) by clicking on the right menu or button. They can all be
run from the command line. Programs that require GUI have to be run
from a terminal opened under a GUI.
Legend:
<> = single special or function key on the keyboard. For example
<Ctrl> indicates the “control” key.
italic = name of the file or variable you probably want to substitute
with your own.
fixed width = in-line Linux commands and filenames.
Notes for the UNIX Clueless:
1. LINUX IS CASE-SENSITIVE. For example: Netscape, NETSCAPE and nEtscape
are three different commands. Also my_filE, my_file, and my_FILE are three
different files. Your user login name and password are also case sensitive.
(This goes with the tradition of UNIX and the “c” programming language
being case sensitive.)
2. Filenames can be up to 256 characters long and can contain letters,
numbers, “.” (dot), “_” (underscore), “-” (dash), plus some other not recommended
characters.
3. Files with names starting with “.” are normally not shown by the
ls
(list) or dir commands. Think of these files as “hidden”. Use
ls -a
(list with the option “all”) to see these files.
4. “/” is an equivalent to DOS “\” (root directory, meaning the parent
of all other directories).
5. Under Linux, all directories appear under a single directory tree
(there are no DOS-style drive letters).
6. In a configuration file, a line starting with # is a comment.
7.1 Linux essential shortcuts and sanity commands
<Ctrl><Alt><F1>
Switch to the first text terminal. Under Linux you can have several
(6 in standard setup) terminals opened at the same time.
<Ctrl><Alt><Fn> (n=1..6)
Switch to the nth text terminal.
tty
Print the name of the terminal in which you are typing this command.
<Ctrl><Alt><F7>
Switch to the first GUI terminal (if X-windows is running on this terminal).
<Ctrl><Alt><Fn> (n=7..12)
Switch to the nth GUI terminal (if a GUI terminal is running on screen
n-1). On default, nothing is running on terminals
8 to 12, but you can run another server there.
<Tab>
(In a text terminal) Autocomplete the command if there is only
one option, or else show all the available options.
THIS SHORTCUT IS GREAT! It even works at LILO prompt!
<ArrowUp>
Scroll and edit the command history. Press <Enter> to execute.
<Shift><PgUp>
Scroll terminal output up. Work also at the login prompt, so you can
scroll through your bootup messages.
<Shift><PgDown>
Scroll terminal output down.
<Ctrl><Alt><+>
(in X-windows) Change to the next X-server resolution (if you set up
the X-server to more than one resolution). For multiple resolutions on
my standard SVGA card/monitor, I have the following line in the file
/etc/X11/XF86Config
(the first resolution starts on default, the largest determines the size
of the “virtual screen”):
Modes "1024x768" "800x600" "640x480" "512x384" "480x300" "400x300"
"1152x864"
<Ctrl><Alt><->
(in X-windows) Change to the previous X-server resolution.
<Ctrl><Alt><BkSpc>
(in X-windows) Kill the current X-windows server. Use if the X-windows
server crushes and cannot be exited normally.
<Ctrl><Alt><Del>
Shut down the system and reboot. This is the normal shutdown command
for a user at the text-mode console. Don’t just press the “reset” button
for shutdown!
<Ctrl>c
Kill the current process (mostly in the text mode for small applications).
<Ctrl>d
Log out from the current terminal. See also the next command.
<Ctrl>d
Send [End-of-File] to the current process. Don’t press it twice else
you also log out (see the previous command).
<Ctrl>s
Stop the transfer to the terminal.
<Ctrl>q
Resume the transfer to the terminal. Try if your terminal mysteriously
stops responding.
<Ctrl>z
Send the current process to the background.
exit
Logout. I can also use logout for the same effect. (If
you have started a second shell, e.g., using bash the second shell
will be exited and you will be back in the first shell, not logged out.)
reset
Restore a screwed-up terminal (a terminal showing funny characters)
to default setting. Use if you tried to “cat” a binary file. You may not
be able to see the command as you type it.
<MiddleMouseButton>
Paste the text which is currently highlighted somewhere else. This
is the normal “copy-paste” operation in Linux. (It doesn’t work with
Netscape and WordPerfect which use the MS Windows-style “copy-paste”. It
does work in the text terminal if you enabled “gpm” service using “setup”.)
Best used with a Linux-ready 3-button mouse (Logitech or similar) or else
set “3-mouse button emulation”).
~
(tilde) My home directory (normally the directory /home/my_login_name).
For example, the command cd ~/my_dir will change my working
directory to the subdirectory “my_dir” under my home directory.
Typing just “cd” alone is an equivalent of the command “cd ~”.
.
(dot) Current directory. For example, ./my_program will attempt
to execute the file “my_program” located in your current working directory.
..
(two dots) Directory parent to the current one. For example, the command
cd
.. will change my current working directory one one level up.
7.2 Common Linux commands–system info
pwd
Print working directory, i.e., display the name of my current directory
on the screen.
hostname
Print the name of the local host (the machine on which you are working).
Use netconf (as root) to change the name of the machine.
whoami
Print my login name.
id
username
Print user id (uid) and his/her group id (gid), effective id (if different
than the real id) and the supplementary groups.
date
Print or change the operating system date and time. E.g., I could change
the date and time to 2000-12-31 23:57 using this command:
date 123123572000
To set the hardware (BIOS) clock from the system (Linux) clock, use
the command (as root) setclock
time
Determine the amount of time that it takes for a process to complete
+ other info. Don’t confuse it with the date command. E.g. I can
find out how long it takes to display a directory content using:
time ls
who
Determine the users logged on the machine.
rwho -a
(=remote who) Determine all users logged on your network. The rwho
service must be enabled for this command to run. If it isn’t, run setup
as root to enable “rwho”.
finger
user_name
System info about a user. Try: finger root
last
Show listing of users last logged-in on your system.
history | more
Show the last (1000 or so) commands executed from the command line
on the current account. The “| more” causes the display to stop after each
screenful.
uptime
Show the amount of time since the last reboot.
ps
(=print status) List the processes currently run by the current user.
ps axu | more
List all the processes currently running, even those without the controlling
terminal, together with the name of the user that owns each process.
top
Keep listing the currently running processes, sorted by cpu usage (top
users first). In KDE, you can get GUI-based Ktop from “K”menu under “System”-”Task
Manager” (or by executing “ktop” in an X-terminal).
uname -a
(= Unix name with option “all”) Info on your (local) server. I can
also use guname (in X-window terminal) to display the info more
nicely.
free
Memory info (in kilobytes).
df -h
(=disk free) Print disk info about all the filesystems (in human-readable
form)
du / -bh | more
(=disk usage) Print detailed disk usage for each subdirectory starting
at the “/” (root) directory (in human legible form).
cat /proc/cpuinfo
Cpu info–it show the content of the file cpuinfo. Note that
the files in the /proc directory are not real files–they are
hooks to look at information available to the kernel.
cat /proc/interrupts
List the interrupts in use.
cat /proc/version
Linux version and other info
cat /proc/filesystems
Show the types of filesystems currently in use.
cat /etc/printcap
Show the setup of printers.
lsmod
(As root. Use /sbin/lsmod to execute this command when you
are a non-root user.) Show the kernel modules currently loaded.
set|more
Show the current user environment.
echo $PATH
Show the content of the environment variable “PATH”. This command can
be used to show other environment variables as well. Use “set” to see the
full environment.
dmesg | less
Print kernel messages (the content of the so-called kernel ring buffer).
Press “q” to quit “less”. Use less /var/log/dmesg to see
what “dmesg” dumped into this file right after the last system bootup.
7.3 Basic operations
any_command
--help |more
Display a brief help on a command (works with most commands). “–help”
works similar to DOS “/h” switch. The “more” pipe is needed if the output
is longer than one screen.
man
topic
Display the contents of the system manual pages (help) on the topic.
Try man man first. Press “q” to quit the viewer. The command info
topic
works similar and may contain more up-to-date information. Manual pages
can be hard to read. Try any_command --help for short,
easy to digest help on a command. If more info needed, have a look to the
directory /usr/doc. To display manual page from a specific section,
I may use something like in this example: man 3 exit (this
displays an info on the command exit from section 3 of the manual
pages).
apropos
topic
Give me the list of the commands that have something to to do with
my topic.
help command
Display brief info on a bash (shell) build-in command.
ls
List the content of the current directory. Under Linux, the command
“dir” is an alias to ls. Many users have “ls” to be an alias to “ls –color”.
ls -al |more
List the content of the current directory, all files (also those starting
with a dot), and in a long form. Pipe the output through the “more” command,
so that the display pauses after each screenful.
cd
directory
Change directory. Using “cd” without the directory name will take you
to your home directory. “cd -” will take you to your previous directory
and is a convenient way to toggle between two directories. “cd ..” will
take you one directory up.
cp
source destination
Copy files. E.g., cp /home/stan/existing_file_name .
will copy a file to my current working directory. Use the “-r” option (for
recursive) to copy the contents of whole directories, e.g. , cp -r
my_existing/dir/ ~ will copy a subdirectory under my current
working directory to my home directory.
mcopy
source destination
Copy a file from/to a DOS filesystem (no mounting necessary). E.g.,
mcopy
a:\autoexec.bat ~/junk . See man mtools for related commands:
mdir, mcd, mren, mmove, mdel, mmd, mrd, mformat ….
mv source destination
Move or rename files. The same command is used for moving and renaming
files and directories.
ln
source destination
Create a hard link called destination to the file called source.
The link appears as a copy of the original files, but in reality only one
copy of the file is kept, just two (or more) directory entries point to
it. Any changes the file are automatically visible throughout. When one
directory entry is removed, the other(s) stay(s) intact. The limitation
of the hard links are: the files have to be on the same filesystem, hard
links to directories or special files are impossible.
ln -s source destination
Create a symbolic (soft) link called “destination” to the file called
“source”. The symbolic link just specifies a path where to look for the
file. In contradistinction to hard links, the source and destination don’t
not have to tbe on the same filesystem. In comparison to hard links, the
drawback of symbolic links are: if the original file is removed, the link
is “broken”, symbolic links can also create circular references (like circular
references in spreadsheets or databases, e.g., “a” points to “b” and “b”
points back to “a”).
rm files
Remove (delete) files. You must own the file in order to be able to
remove it. On many systems, you will be asked or confirmation of deleation,
if you don’t want this, use the “-f” (=force) option, e.g., rm -f *
will remove all files in my current working directory, no questions asked.
mkdir
directory
Make a new directory.
rmdir
directory
Remove an empty directory.
rm -r files
(recursive remove) Remove files, directories, and their subdirectories.
Careful with this command as root–you can easily remove all files on the
system with such a command executed on the top of your directory tree,
and there is no undelete in Linux (yet). But if you really wanted to do
it (reconsider), here is how (as root):
rm -rf /*
cat filename | more
View the content of a text file called “filename”, one page a time.
The “|” is the “pipe” symbol (on many American keyboards it shares the
key with “\”) The pipe makes the output stop after each screenful. For
long files, it is sometimes convenient to use the commands head and tail
that display just the beginning and the end of the file. If you happened
to use “cat” a binary file and your terminal displays funny characters
afterwards, you can restore it with the command “reset”.
less
filename
Scroll through a content of a text file. Press q when done. “Less”
is roughly equivalent to “more” , the command you know from DOS, although
very often “less” is more convenient than “more”.
pico
filename
Edit a text file using the simple and standard text editor called pico.
pico -w filename
Edit a text file, while disabling the long line wrap. Handy for editing
configuration files, e.g. /etc/fstab.
find / -name "filename"
Find the file called “filename” on your filesystem starting the search
from the root directory “/”. The “filename” may contain wildcards (*,?).
locate
filename
Find the file name of which contains the string “filename”. Easier
and faster than the previous command but depends on a database that normally
rebuilds at night.
./program_name
Run an executable in the current directory, which is not on your PATH.
touch
filename
Change the date/time stamp of the file filename to
the current time. Create an empty file if the file does not exist.
xinit
Start a barebone X-windows server (without a windows manager).
startx
Start an X-windows server and the default windows manager. Works like
typing “win” under DOS with Win3.1
startx -- :1
Start another X-windows session on the display 1 (the default is opened
on display 0). You can have several GUI terminals running concurrently.
Switch between them using <Ctrl><Alt><F7>, <Ctrl><Alt><F8>,
etc.
xterm
(in X terminal) Run a simple X-windows terminal. Typing exit
will close it. There are other, more advanced “virtual” terminals
for X-windows. I like the popular ones: konsole and kvt
(both come with kde) and gnome-terminal (comes with gnome).
If you need something really fancy-looking, try Eterm.
xboing
(in X terminal). Very nice, old-fashioned game. Many small games/programs
are probably installed on your system. I also like xboard (chess).
shutdown -h now
(as root) Shut down the system to a halt. Mostly used for a remote
shutdown. Use <Ctrl><Alt><Del> for a shutdown at the console (which
can be done by any user).
halt
reboot
(as root, two commands) Halt or reboot the machine. Used for remote
shutdown, simpler to type than the previous command.
Network apps
netscape
(in X terminal) Run netscape (requires a separate Netscape installation).
The current versions of Netscape (4.x) are known to be big and buggy. They
occasionally crash by vanishing (no other harm done). Also, when not connected
to the network , Netscape likes to refuse to do anything (looks like it
hanged)-it revives when you connect.
netscape -display host:0.0
(in X terminal) Run netscape on the current machine and direct the
output to machine named “host” display 0 screen 0. Your current machine
must have a permission to display on the machine “host” (typically given
by executing the command xhost
current_machine_name in
the xterminal of the machine host. Other X-windows program can be run remotely
the same way.
lynx
file.html
View an html file or browse the net from the text mode.
pine
A good text-mode mail reader. Another good and standard one is elm.
Your Netscape mail will read the mail from your Internet account. pine
will let you read the “local” mail, e.g. the mail your son or a cron process
sends to you from a computer on your home network. The command mail
could also be used for reading/composing mail, but it would be inconvenient–it
is meant to be used in scripts for automation.
elm
A good tex-mode mail reader. See the previous command.
mutt
A really basic but extremally useful and fast mail reader.
A basic operating system tool for e-mail. Look at the previous commands
for a better e-mail reader. mail is good if you wanted to send
an e-mail from a shell script.
licq
(in X term) An icq “instant messaging” client. Another good one is
kxicq.
Older distributions don’t have an icq client installed, you have to do
download one and install it.
talk
username1
Talk to another user currently logged on your machine (or use “talk
username1@machinename“
to talk to a user on a different computer) . To accept the invitation to
the conversation, type the command “talk
username2“. If
somebody is trying to talk to you and it disrupts your work, your may use
the command “mesg n” to refuse accepting messages. You may want
to use “who” or “rwho” to determine the users who are
currently logged-in.
mc
Launch the “Midnight Commander” file manager (looks like “Norton Commander”
for Linux).
telnet
server
Connect to another machine using the TELNET protocol. Use a remote
machine name or IP address. You will be prompted for your login name and
password–you must have an account on the remote machine to login. Telnet
will connect you to another machine and let you operate on it as if you
were sitting at its keyboard (almost). Telnet is not very secure–everything
you type goes in open text, even your password!
rlogin
server
(=remote login) Connect to another machine. The login name/password
from your current session is used; if it fails you are prompted for a password.
rsh
server
(=remote shell) Yet another way to connect to a remote machine. The
login name/password from your current session is used; if it fails you
are prompted for a password.
ftp
server
Ftp another machine. (There is also ncftp which adds extra
features and gftp for GUI .) Ftp is good for copying files to/from
a remote machine. Try user “anonymous” if you don’t have an account on
the remote server. After connection, use “?” to see the list of available
ftp commands. The essential ftp command are: ls (see the
files on the remote system), ASCII,
binary (set the file
transfer mode to either text or binary, important that you select the proper
one ), get (copy a file from the remote system to the local system),
mget
(get many files at once), put (copy a file from the local system
to the remote system), mput (put many files at once), bye
(disconnect). For automation in a script, you may want to use
ncftpput
and ncftpget, for example:
ncftpput -u my_user_name -p my_password -a remote.host.domain remote_dir
*local.html
minicom
Minicom program (looks like “Procomm for Linux”).
File (de)compression
tar -zxvf filename.tar.gz
(=tape archiver) Untar a tarred and compressed tarball (*.tar.gz or
*.tgz) that you downloaded from the Internet.
tar -xvf filename.tar
Untar a tarred but uncompressed tarball (*.tar).
gunzip
filename.gz
Decompress a zipped file (*.gz” or *.z). Use gzip (also zip
or compress) if you wanted to compress files to this file format.
bunzip2
filename.bz2
(=big unzip) Decompress a file (*.bz2) zipped with bzip2 compression
utility. Used for big files.
unzip
filename.zip
Decompress a file (*.zip) zipped with a compression utility compatible
with PKZIP for DOS.
unarj e filename.arj
Extract the content of an *.arj archive.
uudecode -o outputfile filename
Decode a file encoded with uuencode. uu-encoded files
are typically used for transfer of non-text files in e-mail (uuencode transforms
any file into an ASCII file).
7.4 Process control
ps
(=print status) Display the list of currently running
processes with their process IDs (PID) numbers. Use ps axu to
see all processes currently running on your system (also those of other
users or without a controlling terminal), each with the name of the owner.
Use “top” to keep listing the processes currently running.
fg
PID
Bring a background or stopped process to the foreground.
bg
PID
Send the process to the background. Opposite to fg. The same can be
accomplished with <Ctrl>z. If you have stopped jobs, you have
to type exit twice in row to log out.
any_command&
Run any command in the background (the symbol “&” means “run the
proceeding command in the background”).
batch any_command
Run any command (usually one that is going to take more time) when
the system load is low. I can logout, and the process will keep running.
at 17:00
Execute a command at a specified time. You will be prompted for
the command(s) to run, until you press <Ctrl>d.
kill
PID
Force a process shutdown. First determine the PID of the process to
kill using ps.
killall
program_name
Kill program(s) by name.
xkill
(in an xwindow terminal) Kill a GUI-based program with mouse. (Point
with your mouse cursor at the window of the process you want to kill and
click.)
lpc
(as root) Check and control the printer(s). Type “?” to see the list
of available commands.
lpq
Show the content of the printer queue. Under KDE (X-Windows), you may
use GUI-based “Printer Queue” available from “K”menu-Utilities.
lprm
job_number
Remove a printing job “job_number” from the queue.
nice
program_name
Run
program_name adjusting its priority. Since the priority
is not specified in this example, it will be adjusted by 10 (the process
will run slower), from the default value (usually 0). The lower the number
(of “niceness” to other users on the system), the higher the priority.
The priority value may be in the range -20 to 19. Only root may specify
negative values. Use “top” to display the priorities of the running processes.
renice -1 PID
(as root) Change the priority of a running process to -1. Normal users
can only adjust processes they own, and only up from the current value
(make them run slower).
<Ctrl>c, <Ctrl>z, <Ctrl>s, and <Ctrl>q
also belong to this chapter but they were described previously.
In short they mean: stop the current command, send the current command
to the background, stop the data transfer, resume the data transfer.
7.5 Basic administration commands
printtool
(as root in X-terminal) Configuration tool for your printer(s). Settings
go to the file /etc/printcap.
setup
(as root) Configure mouse, soundcard, keyboard, X-windows, system services.
There are many distibution-specific configuration utilities, setup
is the default on RedHat. Mandrake 7.0 offers very nice DrakConf
.
linuxconfig
(as root, either in text or graphical mode). You can access and change
hundreds of setting from it. Very powerful–don’t change too many things
at the same time, and be careful with changing entries you don’t understand.
xvidtune
(in X-terminal). Adjust the settings of the graphical display for all
resolutions so as to eliminate black bands, shift the display right/left/up/down,
etc. (First use the knobs on your monitor to fit your text mode correctly
on the screen.) To make the changes permanent, display the frequencies
on the screen and transfer them to the setup file /etc/X11/XF86Config.
alias ls="ls --color=tty"
Create an alias for the command “ls” to enhance its format with color.
In this example, the alias is also called “ls” and the “color” option is
only envoke when the output is done to a terminal (not to files). Put the
alias into the file /etc/bashrc if you would like the alias to
be always accessible to all users on the system. Type “alias“
alone to see the list of aliases on your system.
adduser
user_name
Create a new account (you must be root). E.g., adduser barbara
Don’t forget to set up the password for the new user in the next step.
The user home directory is
/home/user_name.
useradd
user_name
The same as the command ” adduser
user_name “.
userdel
user_name
Remove an account (you must be a root). The user’s home directory and
the undelivered mail must be dealt with separately (manually because you
have to decide what to do with the files).
groupadd
group_name
Create a new group on your system. Non-essential but can be handy even
on a home machine with a small number of users.
passwd
Change the password on your current account. If you are root, you can
change the password for any user using: passwd
user_name
chmod perm filename
(=change mode) Change the file access permission for the files you
own (unless you are root in which case you can change any file). You can
make a file accessible in three modes: read (r), write (w), execute (x)
to three classes of users: owner (u), members of the same group as the
owner (g), others on the system (o). Check the current access permissions
using:
ls -l filename
If the file is accessible to all users in all modes it will show:
rwxrwxrwx
The first triplet shows the file permission for the owner of the file,
the second for his/her group, the third for others. A “no” permission is
shown as “-”.
E.g., this command will add
the permission to read the file
“junk” to all (=user+group+others):
chmod a+r junk
This command will remove the permission to execute the file junk from
others:
chmod o-x junk
Also try here
for more info.
You can set the default file permissions for the news files that you
create using the command umask (see man umask).
chown
new_ownername filename
chgrp new_groupname filename
Change the file owner and group. You should use these two commands
after you copy a file for use by somebody else.
su
(=substitute user id) Assume the superuser (=root) identity (you will
be prompted for the password). Type “exit” to return you to your previous
login. Don’t habitually work on your machine as root. The root account
is for administration and the su command is to ease your access to the
administration account when you require it. You can also use “su” to assume
any other user identity, e.g. su barbara will make me “barbara”
(password required unless I am a superuser).
kernelcfg
(as root in X terminal). GUI to to add/remove kernel modules. You can
do the same from the command line using the command “insmod“,
but “insmode” is less “newbie-friendly”.
lsmod
List currently loaded kernel modules. A module is like a device driver–it
provides operating system kernel support for a particular piece of hardware
or feature.
modprobe -l |more
List all the modules available for your kernel. The available modules
are determined by how your Linux kernel was compliled. Every possible module/feature
can be compiled on linux as either “hard wired” (fast, non-removable),
“module” (maybe slower, but loaded/removable on demand), or “no” (no support
for this feature at all).
insmod parport
insmod ppa
(as root) Insert modules into the kernel (a module is roughly an equivalent
of a DOS device driver). This example shows how to insert the modules for
support of the external parallel port zip drive (it appears to be a problem
to get the external zip drive to work in any other way under RH6.0
).
rmmod
module_name
(as root, not essential). Remove the module module_name from
the kernel.
setserial /dev/cua0 port 0x03f8 irq 4
(as root) Set a serial port to a non-standard setting. The example
here shows the standard setting for the first serial port (cua0 or ttyS0).
The standard PC settings for the second serial port (cua1or ttyS1) are:
address of i/o port 0x02f8, irq 3. The third serial port (cua2 or ttyS2):
0x03e8, irq 4. The forth serial port (cua3 or ttyS3): 0x02e8, irq 3. Add
your setting to /etc/rc.d/rc.local if you want it to be set at
the boot time. See man setserial for good a overview.
fdisk
(as root) Linux hard drive partitioning utility (DOS has a utility
with the same name).
cd /usr/src/linux-2.0.36
make xconfig
(as root in X terminal). Nice GUI front-end for configuration of the
kernel options in preparation for compilation of your customized kernel.
(The directory name contains the version of your Linux kernel so you may
need to modify the directory name if your Linux kernel version is different
than 2.0.36 used in this example. You also need the “Tk” interpreter and
the kernel source code installed. ) The alternatives to “make xconfig”
are: “make config” (runs a scripts that asks you questions in the
text mode) and “make menuconfig” (runs a text-based menu-driven configuration
utility). Try: less /usr/doc/HOWTO/Kernel-HOWTO for more information.
After the configuration, you may choose to proceed with kernel
compilation of the new kernel by issuing the following commands:
make dep
make zImage
The last command will take some time to complete (maybe 0.5 h, depending
on your hardware). It produces the file “zImage”, which is your new Linux
kernel. Next:
make modules
make modules_install
Read: /usr/doc/HOWTO/Kernel-HOWTO for information on how to install
the new kernel. You will probably also find it useful to read “man depmode”.
Configuration, compilation and installation of a new kernel is not difficult
but it CAN lead to problems if you don’t know what you are doing.
Compilation of a kernel is a good way to test your hardware, because
it involves a massive amount of computing. If your hardware is “flaky”,
you will most likely receive the “signal 11″ error (read the beatiful
/usr/doc/FAQ/txt/GCC-SIG11-FAQ).
See
this
for details on kernel upgrade.
depmod -a
(as root) Build the module dependency table for the kernel. This can,
for example, be useful after installing and booting a new kernel. Use “modprobe
-a” to load the modules.
ldconfig
(as root) Re-create the bindings and the cache for the loader of dynamic
libraries (“ld”). You may want to run ldconfig after an installation of
new dynamically linked libraries on your system. (It is also re-run every
time you boot the computer, so if you reboot you don’t have to run it manually.)
mknod /dev/fd0 b 2 0
(=make node, as root) Create a device file. This example shows how
to create a device file associated with your first floppy drive and could
be useful if you happened to accidentally erase it. The options are: b=block
mode device (c=character mode device, p=FIFO device, u=unbuffered character
mode device). The two integers specify the major and the minor device number.
fdformat /dev/fd0H1440
mkfs -c -t ext2
(=floppy disk format, two commands, as root) Perform a low-level formatting
of a floppy in the first floppy drive (/dev/fd0), high density (1440 kB).
Then make a Linux filesystem (-t ext2), checking/marking bad blocks (-c
). Making the files system is an equivalent to the high-level format.
badblocks /dev/fd01440 1440
(as root) Check a high-density floppy for bad blocks and display the
results on the screen. The parameter “1440″ specifies that 1440 blocks
are to be checked. This command does not modify the floppy.
fsck -t ext2 /dev/hda2
(=file system check, as root) Check and repair a filesystem. The example
uses the partition hda2, filesystem type ext2.
dd if=/dev/fd0H1440 of=floppy_image
dd if=floppy_image of=/dev/fd0H1440
(two commands, dd=”data duplicator”) Create an image of a floppy to
the file called “floppy_image” in the current directory. Then copy floppy_image
(file) to another floppy disk. Works like DOS “DISKCOPY”.
Program installation
rpm -ivh filename.rpm
(=RedhatPackageManager, install, verbose, hashes displayed to show
progress, as root.) Install a content of RedHat rpm package(s) and print
info on what happened. Keep reading if you prefer a GUI installation.
rpm -qpi filename.rpm
(=RedhatPackageManager, query, package, list.) Read the info on the
content of a yet uninstalled package
filename.rpm.
rpm -qpl filename.rpm
(=RedhatPackageManager, query, package, information.) List the files
contained in a yet uninstalled package
filename.rpm.
rpm -qf filename
(=RedhatPackageManager, query, file.) Find out the name of the *.rpm
package to which the file
filename (on your hardrive) belongs.
rpm -e packagename
(=RedhatPackageManager, erase=uninstall.) Uninstall a package pagckagename.
Packagname
is the same as the beginning of the *.rpm package file but without the
dash and version number.
kpackage
gnorpm
glint
(in X terminal, as root if you want to be able to install packages)
GUI fronts to the Red Hat Package Manager (rpm). “glint” comes with RH5.2,
“gnorpm” with RH6.0, “kpackage” comes with RH6.1 or must be installed separately
but is the best of the three. Use any of them to view which software packages
are installed on your system and the what not-yet-installed packages are
available on your RedHat CD, display the info about the packages, and install
them if you want (installation must be done as root).
Accessing drives/partitions
mount
See
here
for details on mounting drives. Examples are shown in the next commands.
mount -t auto /dev/fd0 /mnt/floppy
(as root) Mount the floppy. The directory /mnt/floppy must
exist, be empty and NOT be your current directory.
mount -t auto /dev/cdrom /mnt/cdrom
(as root) Mount the CD. You may need to create/modify the /dev/cdrom
file depending where your CDROM is. The directory /mnt/cdrom must
exist, be empty and NOT be your current directory.
mount /mnt/floppy
(as user or root) Mount a floppy as user. The file /etc/fstab
must be set up to do this. The directory
/mnt/floppy must not
be your current directory.
mount /mnt/cdrom
(as user or root) Mount a CD as user. The file /etc/fstab
must be set up to do this. The directory
/mnt/cdrom must not be
your current directory.
umount /mnt/floppy
Unmount the floppy. The directory
/mnt/floppy must not be
your (or anybody else’s) current working directory. Depending on your setup,
you might not be able to unmount a drive that you didn’t mount.
7.6 Network administration tools
netconf
(as root) A very good menu-driven setup of your network.
pingmachine_name
Check if you can contact another machine (give the machine’s name or
IP), press <Ctrl>C when done (it keeps going).
route -n
Show the kernel routing table.
nslookup
host_to_find
Query your default domain name server (DNS) for an Internet name (or
IP number) host_to_find. This way you can check if your DNS works.
You can also find out the name of the host of which you only know the IP
number.
traceroute host_to_trace
Have a look how you messages trave to host_to_trace
(which is either a host name or IP number).
ipfwadm -F -p m
(for RH5.2, seen next command for RH6.0) Set up the firewall IP forwarding
policy to masquerading. (Not very secure but simple.) Purpose: all computers
from your home network will appear to the outside world as one very busy
machine and, for example, you will be allowed to browse the Internet from
all computers at once.
echo 1 > /proc/sys/net/ipv4/ip_forward
ipfwadm-wrapper -F -p deny
ipfwadm-wrapper -F -a m -S xxx.xxx.xxx.0/24 -D 0.0.0.0/0
(three commands, RH6.0). Does the same as the previous command. Substitute
the “x”s with digits of your class “C” IP address that you assigned
to your home network. See
here
for more details. In RH6.1, masquarading seems broken to me–I think I
will install Mandrake Linux:).
ifconfig
(as root) Display info on the network interfaces currently active
(ethernet, ppp, etc). Your first ethernet should show up as eth0, second
as eth1, etc, first ppp over modem as ppp0, second as ppp1, etc. The “lo”
is the “loopback only” interface which should be always active. Use the
options (see ifconfig --help) to configure the interfaces.
ifup interface_name
(/sbin/ifup to it run as a user) Startup a network interface.
E.g.:
ifup eth0
ifup ppp0
Users can start up or shutdown the ppp interface only when the right
permission was checked during the ppp setup (using netconf ).
To start a ppp interface (dial-up connection), I normally use kppp available
under kde menu “internet”.
ifdown
interface_name
(/sbin/ifdown to run it as a user). Shut down the network
interface. E.g.: ifdown ppp0 Also, see the previous command.
netstat | more
Displays a lot (too much?) information on the status of your network.
Music-related commands
cdplay play 1
Play the first track from a audio CD.
eject
Get a free coffee cup holder 
)). (Eject the CD
ROM tray).
play my_file.wav
Play a wave file.
mpg123 my_file.mp3
Play an mp3 file.
mpg123 -w my_file.wav my_file.mp3
Create a wave audio file from an mp3 audio file.
knapster
(in X terminal) Start the program to downolad mp3 files that other
users of napster have displayed for downloading. Really cool!
cdparanoia -B "1-"
(CD ripper) Read the contents of an audio CD and save it into
wavefiles in the current directories, one track per wavefile. The
“1-”
means “from track 1 to the last”. -B forces putting each track into
a separate file.
playmidi my_file.mid
Play a midi file. playmidi -r my_file.mid
will display text mode effects on the screen.
sox
(argument not given here) Convert from almost any audio file format
to another (but not mp3s). See man sox.
Graphics-related commands
kghostview my_file.ps
Display a postscript file on screen. I can also use the older-looking
ghostview
or gv for the same end effect.
ps2pdf my_file.ps my_file.pdf
Make a pdf (Adobe portable document format) file from a postscript
file.
gimp
(in X terminal) A humble looking but very powerful image processor.
Takes some learning to use, but it is great for artists, there is almost
nothing you can’t do with gimp. Use your mouse right button to get local
menus, and learn how to use layers. Save your file in the native gimp file
format *.xcf (to preserve layers) and only then flatten it and save as
png (or whatever). There is a large user manual /usr/
gphoto
(in X terminal) Powerful photo editor.
giftopnm my_file.giff > my_file.pnm
pnmtopng my_file.pnm > my_file.png
Convert the propriatory giff graphics into a raw, portable pnm file.
Then convert the pnm into a png file, which is a newer and better standard
for Internet pictures (better technically plus there is no danger
of being sued by the owner of giff patents).
