Bring a background or stopped process to the foreground.
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.
Run any command in the background (the symbol "&" means "run the proceeding command in the background").
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.
Execute a command at a specified time. You will be prompted for the command(s) to run, until you press <Ctrl>d.
Force a process shutdown. First determine the PID of the process to kill using ps.
Kill program(s) by name.
(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.)
(as root) Check and control the printer(s). Type "?" to see the list of available commands.
Show the content of the printer queue. Under KDE (X-Windows), you may use GUI-based "Printer Queue" available from "K"menu-Utilities.
Remove a printing job "job_number" from the queue.
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.
(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 .
(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.
(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.
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.
The same as the command " adduser 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).
Create a new group on your system. Non-essential but can be handy even on a home machine with a small number of users.
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:
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.
(=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).
(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".
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).
(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 ).
(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.
(as root) Linux hard drive partitioning utility (DOS has a utility with the same name).
(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:
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:
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.
(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.
(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.
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".
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.
(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).
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.
(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.
(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.
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.
Check if you can contact another machine (give the machine's name or IP), press <Ctrl>C when done (it keeps going).
Show the kernel routing table.
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.
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:).
(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.
(/sbin/ifup to it run as a user) Startup a network interface. E.g.:
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".
(/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.
Get a free coffee cup holder :))). (Eject the CD ROM tray).
Play a wave file.
Play an mp3 file.
mpg123 -w my_file.wav my_file.mp3
Create a wave audio file from an mp3 audio file.
(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.
Play a midi file. playmidi -r my_file.mid will display text mode effects on the screen.
(argument not given here) Convert from almost any audio file format to another (but not mp3s). See man sox.
ps2pdf my_file.ps my_file.pdf
Make a pdf (Adobe portable document format) file from a postscript file.
(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/
(in X terminal) Powerful photo editor.