Linux Basics and Tips

On this page, I (and many others) just wrote some stuff that did not deserve (or need) their own section because of their simple nature. I suggest anyone new to Linux and Unix read this section so that you will jump in with enough knowledge. You probably have a lot more to add to this, so make sure you e-mail it to me to help more people.

• Free Space:
  To find out how much disk space you have left on your hard drive or mounted floppy drive, type df.
• Program Info:
  For details about using a program you can use the "man" command to access the manual page for that particular program. For a description of the command "ls" you would type man ls. Some programs do not have manual pages ("manpages"), and there are manpages that aren't really much help. However, as you get more advanced with Linux you will find manual pages to be an invaluable resource. Mark Schreiber wants to remind us of the info command as well. Use info when looking for Texinfo documentation.
• Deleting Directories:
  To remove an entire directory without being prompted if you want to delete each file, type rm -rf directory-name, where "directory-name" is the name of the directory. Be careful with this! (Also works with the cp (copy) command, when you overwrite old files.) In case you're wondering, the r is for recursive (moves through subdirectories) and the f stands for force.
• Copying Entire Directory Trees:
  To copy an entire directory tree, preserving all permissions, you could do something like:

  cd /source/directory/
  cp -ap . /path/to/dest/
  

  However, this can take a while for large trees with lots of small files (i.e. large source trees). Perhaps a better way would be:

  cd /source/directory/
  tar cpf - . | tar xvf - -C /path/to/dest/
  

  The advantage of this method (especially copying between physical drives, or different machines as we'll see in a moment) is speed. The 'cp' command will read one file from the source, and write to the destination, rinse repeat, ad nauseum until the entire tree is copied. Tar, on the other hand, will read from the source as fast as it can fill up the machine's memory. The second tar command will empty files from memory to disk as quickly as possible, making for a much more efficient overall process. Another advantage of this approach is that it can be used to copy between machines over ssh:

  cd /source/directory/
  tar cpf - . | ssh dest_machine tar xvf - -C /path/to/dest/
  

  This will print a list of files as they are being written to the destination. Together with password-less ssh authentication (using public/private keys), this can be used as a fairly efficient method of syncing up passwd files, dns zones, mirror sites, or simply critical data from many machines which must be backed up to tape, cd, etc..
• Shutting Down:
  Shut down your system properly. Use the command shutdown -h now as root. If you want to reboot, type reboot or shutdown -r now. Mark Schreiber reminds us that the Ctrl-Alt-Delete combination works as well, and does not require a root login.
• Pipes:
  Pipes provide a way to get the output of one command into another command. For instance, if you want to see what's in a very large directory, you can see a screenful at a time by piping the output of ls into less. To do that, just separate the commands with the "pipe" symbol, which is usually [Shift - Backslash]. Try it by typing this:
  ls | less
  Here's another example that uses two pipes to sort the directory listing in reverse alphabetical order:
  ls | sort -r | less
  (Paul Winkler, slinkp@angelfire.com)
• Redirection:
  Redirection is related to the idea of Pipes. Pipes "redirect" the output of a command into the input of another command, but you can also redirect output to a file (or even a device). To redirect the output of a command, use the "<" symbol. One of the most common uses of redirection is to save a directory listing:
  ls > listing.txt
  (Paul Winkler, slinkp@angelfire.com)
• Checking File Integrity:
  Use md5sum (or md5 if you don't have that) to check whether a file is exactly the same as where you transferred it from. Just run md5sum filename and it should give you a string of letters and numbers. This is useful for doing stuff across different systems where you have transferred a file. If the results of md5sum on the same file are different, then the file got corrupted or modified somehow, and you don't want that. You want them to be the same.

• Finding Stuff:
  Find any file on your system by typing find / -name <name>. The "/" is telling it to start from "/" and search everything under that, which is everything on your filesystem. In place of "name" put the name of the file you want to look for. You can also use "*name*" to find anything with the string "name" in its filename, for example.
• MOTD:
  When a user logs in, you can edit /etc/motd to print out a message on their screen. That file must be edited when you are root. Just type in the plain text you want to display when someone logs in.
• Do not IRC as root:
  Do not log on to IRC as root. Even if Nobody decides to try to penetrate your system, you are going to be banned from a lot of the good technical help channels and servers.
• Bailing Out:
  If you're stuck in a program that won't respond, try the "Ctrl-c" combination. In many cases even that won't work, so use "Ctrl-z" to force it to stop. It's best to exit the program the proper way, though.
• Managing RPMs:
  In any distribution that uses the Red Hat package manager (Red Hat, Caldera, and TurboLinux are a few) you can just use the rpm command to install it from your CD. Use rpm -i <filename> to install a package; rpm -U <filename> to upgrade a package; and rpm -i --force <filename> if you installed a package, but didn't use rpm to remove it and want to reinstall it. The file name should end in "*.rpm". If rpm doesn't work on your system then you don't have it installed.
• Upper-case to Lower-case:
  This little script renames all the stuff in a directory to lowercase... for x in *; do mv $x `echo $x | tr [A-Z] [a-z]`; done. (code by Warren Blumenow)
• More Managing RPMs:
  To find out if you have an RPM package installed, the syntax is rpm -qa | grep "part_of_package_name".
• Boot Scripts:
  The startup scripts are usually located in /etc/rc.d/. Inside that directory you may find files such as rc.local, rc.sysinit, rc.serial, and even some subdirectories. The files contained in there may vary with each distribution. If you want to start a program when Linux boots, you probably want to put it in the rc.local file.
• Continuing FTP:
  To continue downloading an incomplete/interrupted file in FTP, use reget <filename> after logging in to the FTP server.
• Finding Text in Files:
  To search for a text string, the basic syntax is grep "text string" /directory/you/want/to/start/searching/from. If you don't want it to be case sensitive then use grep -i "text string" /directory/to/start".
• Exiting vi:
  To exit from vi, the standard text editor, type [ESC], : and then q. Typing : will put you in command mode; wq will quit and write any changes to the file; [ESC] i will put you back in insert mode so that you can type text in.
• Red Hat Oopsies:
  Regularly check the Red Hat Errata pages for updates to your Red Hat distribution. The URL is http://www.redhat.com/support/docs/errata.html.
• Fresh Meat:
  Check for Linux software updates at FreshMeat. Or, join and subscribe to the mailing list to have the day's announcements mailed to you every night.
• Filename Completion:
  Tab filename completion allows you to type in portions of a filename or program, and then press [TAB], and it will complete the filename for you. If there's more than one file or program that starts with what you already typed in, it will beep, and then when you press [TAB] again it lists all the files that start with what you initially type. Play around with it a little bit to see what its limits are, how it can work for what you do, etc.
• ifconfig:
  You can check to see what your current IP addresses are using the ifconfig command.
• HOWTO-reading HOWTO:
  When looking through a Linux HOWTO, try to read only what you think you'll need. If you're still confused, then try additional portions of the HOWTO that you think will be helpful. This is useful if you've figured out part of the problem and want to know how to do the rest.
• How big is it, anyway?:
  To find out how much space a directory and its contents take up, use the command du -b --total to give you the output in bytes. There's a lot more you can do with this command, just read the manpage using man du. Another good trick is to do du -b | sort +0n -r > foo-du.txt, then use less to look for really big files.
• Development packages:
  In case you decided to skip installing development packages during the installation of your distribution, and now can't compile source into binaries that you can use ("command not found" when you're following the guides on this page), install the following packages: autoconf, automake, make, gcc, egcs, glibc, glibc-devel, kernel-headers, libstdc++, XFree86-devel, and binutils. This will probably vary depending on your distribution, but they're basically what you'll need. (Based on experiments performed on Parker Mead)
• Long Filenames:
  Linux can handle long filenames--with spaces, too! However, it's not a good idea to use spaces in filenames, as it creates problems for many programs. To refer to them you'll have to use quotation marks. So if I have a file called That report I was working on then I'll have to edit it using pico "That report I was working on".
• ^D:
  Pressing ^D (Ctrl-D) on an empty line will close that shell, either with the exit or logout command, whichever is appropriate. When you've already typed something, and then you press ^D, you'll see a list of filenames that start with the thing you typed! (Sybren Stuvel)
• How Do I...?:
  When you know what you want to do but not what command you need, try typing apropos subject. This will print out a list of all the man pages having to do with subject. (Paul Winkler)
• Instant Replay:
  Another nice bash feature: typing !string will execute the most recent command that began with string. (Paul Winkler) If you type !?string then it will redo the last command with <string>> anywhere in the command. I think this is a more useful version as it makes it easier to make the last command lookup search pattern more unique. (Rob Denison)
• ^Z:
  ^Z (Control-z) stops a job. After stopping a job, you can do two things with it - start it again in the foreground or start it again in background. To start the job in foreground again, use fg n; to start the job in background use bg n, where n is the job number. jobs will list all the jobs (along with numbers) you currently have running. Note that "all the jobs you currently have running" is only on the current tty - if you're logged in as joe on tty1 and tty2, and you stop a job on tty2, you can't do anything to it from tty1 (play with the jobs, bg and fg commands - you'll see what I mean). Also note that job numbers are not the same as process id (PID) numbers, so DON'T TRY "kill 2" WHEN 2 IS THE JOB NUMBER FOR ANYTHING. (Instead, try kill %2. Thanks to Mark Schreiber for this one.) If you have many jobs running background and make the simple mistake of killing a job number instead of a PID, you risk having some large nasty problems. Trust me on that one. Why? Because a lot of very important processes are loaded with very low PIDs, and it's a bad idea to be signalling them without a good reason. (jbm)
• No more root Logins:
  To never have to log on as root again (having to log on as root is generally looked down upon as a bad practice), try two very useful utilities: su and sudo. "su" allows users to become the superuser if they know the superuser password. Simply type su - at the prompt (the "-" is so that it will discard the PATH variable by the user you're using to become the superuser; this means it is almost exactly like having a root login), and the program will ask for the password. Enter it in, and poof - your $ is now a #. Type exit to get back to being a normal user. (Note: you can also use su - username; "su" will prompt you for "username"'s password. If you are a superuser, you can just do su - username and it won't prompt for a password. Use "exit" to get back to being your usual self). This is very useful for installing system-wide programs, or moving things around. (jbm)
• Less is More:
  Most of the new Linux distributions come with a version of less that will automagically handle gzip'd and zip'd files. This means you can just do less my-big-gzipped-text-file.gz and it will act just like normal less! (Otherwise, try zless.) Also, less can read the directory structure of tar files - gzip'd ones, too. So to make sure that new package you got actually creates its own directory, do less foobar-1.0.tar.gz to see where all it puts things; it'll spit out a listing somewhat like ls -l. (jbm)
• Screenshots:
  To grab a screenshot in X, use xv. Open up xv and click "grab". Set the delay to 5 seconds and check "Hide XV windows". Click Grab and then click on the root window (your desktop) and leave the mouse cursor over the desktop (not over a window). The edge of your screen will blink and your computer will beep to tell you it's grabbed the screenshot. Move the xv window a little bit, and suddenly your whole screen will be filled with the screenshot image. Right-click on that to bring up the control window, and save the image. (jbm) You can also use the import command from the ImageMagick package. Just type this in an xterm: import foobar.jpeg and then click on the window you want to grab. You can do other formats than jpeg, too. To grab the whole screen, just do import -window root wholescreen.jpg. You can do a lot of other tricks, like leaving out window borders, delaying a number of seconds, grabbing a sequence of images to make an animated GIF, etc. See man import. (Paul Winkler, slinkp@angelfire.com.

Got any tips of your own to add? Let me know and your name and a link to your e-mail address or website will be included.

Copyright © 1997-1999 Joshua Go (joshuago at users dot sourceforge dot net). All rights reserved. Permission to use, distribute, and copy this document is hereby granted. You may modify this document as long as credit to me is given.