07-02-2009 11:39 PM - edited 03-01-2019 04:22 PM
Files
A simple description of the UNIX system, also applicable to Linux, is this:
"On a UNIX system, everything is a file; if something is not a file, it is a process."
Sorts of files
Most files are just files, called regular files; they contain normal data, for example text files, executable files or programs, input for or output from a program and so on. While it is reasonably safe to suppose that everything you encounter on a Linux system is a file, there are some exceptions.
File types in a long list
Symbol | Meaning | |
- | Regular file | |
d | Directory | |
l | Link | |
c | Special file | |
s | Socket | |
p | Named pipe | |
b | Block device |
FILE command
WHICH command
LOCATE command
FIND command (-name , -size +5000k) find . -name "*.tmp" -exec rm {} \; find `/home/abhi.` -name *.mp3
GREP command grep -a find .bash_history grep penguin /usr/share/dict/words
chown / chmod / chgrp
wc
File protection with chmod Command Meaning chmod 400 file To protect a file against accidental overwriting. chmod 500 directory To protect yourself from accidentally removing, renaming or moving files from this directory. chmod 600 file A private file only changeable by the user who entered this command. chmod 644 file A publicly readable file that can only be changed by the issuing user. chmod 660 file Users belonging to your group can change this file, others don't have any access to it at all. chmod 700 file Protects a file against any access from other users, while the issuing user still has full access. chmod 755 directory For files that should be readable and executable by others, but only changeable by the issuing user. chmod 775 file Standard file sharing mode for a group. chmod 777 file Everybody can do everything to this file.
At the time a new file is created, it gets a free inode. In that inode is the following information:
*
Owner and group owner of the file.
*
File type (regular, directory, ...)
*
Permissions on the file Section 3.4.1
*
Date and time of creation, last read and change.
*
Date and time this information has been changed in the inode.
*
Number of links to this file (see later in this chapter).
*
File size
*
An address defining the actual location of the file data.
The only information not included in an inode, is the file name and directory. These are stored in the special directory files. By comparing file names and inode numbers, the system can make up a tree-structure that the user understands. Users can display inode numbers using the -i option to ls. The inodes have their own separate space on the disk.
- Absolute and relative paths
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 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.
Key combinations in Bash
Key or key combination Function
Ctrl+A Move cursor to the beginning of the command line.
Ctrl+C End a running program and return the prompt, see Chapter 4.
Ctrl+D Log out of the current shell session, equal to typing exit or logout.
Ctrl+E Move cursor to the end of the command line. Ctrl+H Generate backspace character.
Ctrl+L Clear this terminal.
Ctrl+R Search command history, see Section 3.3.3.4.
Ctrl+Z Suspend a program, see Chapter 4. ArrowLeft and ArrowRight Move the cursor one place to the left or right on the command line, so that you can insert characters at other places than just at the beginning and the end. ArrowUp and ArrowDown Browse history. Go to the line that you want to repeat, edit details if necessary, and press Enter to save time.
Shift+PageUp and Shift+PageDown Browse terminal buffer (to see text that has "scrolled off" the screen). Tab Command or filename completion; when multiple choices are possible, the system will either signal with an audio or visual bell, or, if too many choices are possible, ask you if you want to see them all. Tab Tab Shows file or command completion possibilities.
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.
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 deletion, 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 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 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.
elm A good tex-mode mail reader. See the previous command.
mutt A really basic but extremlly useful and fast mail reader.
mail 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.
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.
wall
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 / ssh 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
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).
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.
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.
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 abhi 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 new 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 abhi will make me "abhi" (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
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).
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.)
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.
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.
Accessing drives/partitions mount
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.
Network administration tools
netconf (as root) A very good menu-driven setup of your network.
ping machine_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.
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.
VI Basics: Basic operations
These are some popular vi commands:
* n dd will delete n lines starting from the current cursor position.
*n dw will delete n words at the right side of the cursor.
*x will delete the character on which the cursor is positioned
*:n moves to line n of the file.
*:w will save (write) the file
*:q will exit the editor.
*:q! forces the exit when you want to quit a file containing unsaved changes.
*:wq will save and exit
*:w newfile will save the text to newfile.
*:wq! overrides read-only permission (if you have the permission to override permissions, for instance when you are using the root account.
*/astring will search the string in the file and position the cursor on the first match below its position.
*/ will perform the same search again, moving the cursor to the next match.
*:1, $s/word/anotherword/g will replace word with anotherword throughout the file.
* yy will copy a block of text.
*n p will paste it n times.
:recover will recover a file after an unexpected interruption.
MISC
BOOT Process - MBR - Init - RC
chkconfig
nice
at and cron
redirection
> >> << < less --help | grep -i examine
who -r
Use clear to clear the command prompt
Use passwd to change your current password
pstree, list the processes in a tree format.
There are three types of I/O, which each have their own identifier, called a file descriptor:
*standard input: 0
*standard output: 1
*standard error: 2
In the following descriptions, if the file descriptor number is omitted, and the first character of the redirection operator is <, the redirection refers to the standard input (file descriptor 0). If the first character of the redirection operator is >, the redirection refers to the standard output (file descriptor 1).
Some practical examples will make this more clear:
ls > dirlist 2>&1
will direct both standard output and standard error to the file dirlist, while the command
ls 2>&1 > dirlist
will only direct standard output to dirlist. This can be a useful option for programmers.
echo $?
pgrep, instead of:
split, have a large file that you need to split into smaller chucks? A mysqldump maybe? split is your command. Below I split a 250MB file into 2 megabyte chunks all starting with the prefix LF_.
-rw-r--r-- 1 root root 251M Feb 19 10:27 largefile
-rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_aa -rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ab -rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ac -rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ad -rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ae
126
portmap 2587 rpc 4u IPv4 5544 TCP *:sunrpc (LISTEN) rpc.statd 2606 root 6u IPv4 5585 TCP *:668 (LISTEN) sshd 2788 root 3u IPv6 5991 TCP *:ssh (LISTEN) sendmail 2843 root 4u IPv4 6160 TCP badhd:smtp (LISTEN) vsftpd 9337 root 3u IPv4 34949 TCP *:ftp (LISTEN) cupsd 16459 root 0u IPv4 41061 TCP badhd:ipp (LISTEN) sshd 16892 root 3u IPv6 61003 TCP badhd.mshome.net:ssh->kontiki.mshome.net:4661 (ESTABLISHED)
Say you want to change your password, but you don't know the command to do it. You can use the man command plus the keyword flag, -k, to search by keyword password for relevant commands:
man -k password passwd passwd (1) - change login password pwck pwck (1m) - password/group file checkers vipw vipw (1b) - edit the password file
If you really can't figure out the name of the command, but you know the name of the package the program came in, try this to list the programs in a package:
rpm -ql packagename | grep bin
Q: What is a runlevel? A: A runlevel is a number which indicates what "mode" you want to computer to boot into. For example, runlevel 5 is graphical mode, where runlevel 3 is text-only mode. Runlevel 1 is "single-user" mode, used for troubleshooting problems.
How do I run something when the computer starts?
service servicename status
service servicename start
service servicename stop
1. Open the ntsysv program: ntsysv
2. Find your service in the list and press space to enable it. Services marked with a * will start automatically at boot.
1. Open the ntsysv program: ntsysv
Q: What is rescue mode and how do I boot into it? A: Rescue mode provides the ability to boot a small Fedora environment entirely from a CD-ROM or USB drive instead of the system's hard drive. As the name implies, rescue mode is provided to rescue you from something. In rescue-mode you can mount and edit your files, such as configuration files and by doing so solve your problems.
To boot into rescue mode, you must be able to boot the system using one of the following methods:
1. By booting the system from an installation boot CD-ROM, or a boot image on a USB disk.
2. By booting the system from the Fedora CD-ROM #1.
Once you have booted using one of the described methods, enter the following command at the installation boot prompt:
linux rescue
shutdown Shuts the system down. shutdown -h now Shuts the system down to halt immediately. shutdown -r now Shuts the system down immediately and the system reboots. whereis Show where the binary, source and manual page files are for a command whereis ls Locates binaries and manual pages for the ls command.
Command Meaning bash GNU shell program. cat file(s) Send content of file(s) to standard output. cd directory Enter directory. cd is a bash built-in command. chgrp newgroup file(s) Change the group ownership of file(s) to newgroup chmod mode file(s) Change access permissions on file(s) chown newowner[:[newgroup]] file(s) Change file owner and group ownership. cp sourcefile targetfile Copy sourcefile to targetfile. df file Reports on used disk space on the partition containing file. echo string Display a line of text export Part of bash that announces variables and their values to the system. file filename Determine file type of filename. find path expression Find files in the file system hierarchy grep PATTERN file Print lines in file containing the search pattern. head file Send the first part of file to standard output id Prints real and effective user name and groups. info command Read documentation about command. less file View file with a powerful viewer. ln targetfile linkname Make a link with name linkname to targetfile. locate searchstring Print all accessible files matching the search pattern. ls file(s) Prints directory content. man command Format and display online (system) manual pages for command. mkdir newdir Make a new empty directory. mv oldfile newfile Rename or move oldfile. newgrp groupname Log in to a new group. pwd Print the present or current working directory. quota Show disk usage and limits. rm file Removes files and directories. rmdir file Removes directories. tail file Print the last part of file. umask [value] Show or change new file creation mode. wc file Counts lines, words and characters in file. which command Shows the full path to command.
Controlling processes (part of) command Meaning regular_command Runs this command in the foreground. command & Run this command in the background (release the terminal) jobs Show commands running in the background. Ctrl+Z Suspend (stop, but not quit) a process running in the foreground (suspend). Ctrl+C Interrupt (terminate and quit) a process running in the foreground. %n Every process running in the background gets a number assigned to it. By using the % expression a job can be referred to using its number, for instance fg %2. bg Reactivate a suspended program in the background. fg Puts the job back in the foreground. kill End a process (also see Shell Builtin Commands in the Info pages of bash)
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