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Basic Linux commands

Robert Lakatos • 2006

Contents

• Useful websites
• Account management
• Exiting from a shell prompt
• Filesystem navigation
• Searching for files by name
• Searching through contents of files
• Determining file types
• Viewing text files
• Editing text files
• Compressing and decompressing files
• Reading compressed text files
• Archiving (packaging) files and directories
• Managing print jobs
• Using floppy diskettes and CD-ROMs
• Remote access
• Running applications in the background
• Processes and disk space
• Command-line history, I/O redirection, and piping
• Miscellaneous
• Starting applications
• Viewer applications
• Converting between document formats
• Image manipulation from a shell prompt

Useful websites

• Chapter 13 of the Red Hat Getting Started Guide
• Unix Commands Help
• Help with Unix
• Linux keyboard shortcuts
• File types and extensions
• Netpbm

Account management

• quota — to check your network account quota.
• yppasswd — to change your network account password.
• passwd — to change your local password.
• chmod [options] filename — to change file permissions.

Exiting from a shell prompt (to close a terminal window or to log out)

• exit
• or by pressing <ctrl+d> — the general end of text control character.

Filesystem navigation

We have a tutorial on manipulating files.

• pwd [options] — to obtain/print the name of your current/working directory.
• cd [options] [directoryname | ~ | ./ | ../ | - ] — to change your working directory.
  Examples:
  • cd /tmp: uses an absolute path
  • cd ~: go to your home directory
  • cd ./subdir: uses a relative path
  • cd ..: go to the parent directory of the current directory
  • cd -: go to the last directory you were in before this one (i.e. go back), with one level of undo. See also the on-line documentation for the pushd, popd, and dirs commands.
• ls [options] directoryname — to list the contents of directories.
  Some useful options (see man ls for more):
  • ls -l: long listing.
  • ls -d */: show only subdirectories of the current directory; don't show files.
  • ls -a: show files beginning with a ., which aren't otherwise shown.
  • ls -lrt: show files sorted by modification time, newest last.
  • ls -lrS: show files sorted by size, biggest last.
• mkdir [options] directoryname — to create new directories.
• rmdir [options] directoryname — to remove/delete directories.
• cp [options] source destination — to copy files and directories.
• mv [options] source destination — to move files and directories.
• rm [options] filenamelist — to remove/delete files.

Searching for files by name

• locate [options] <searchstring>
• find [options] <searchstring>

Searching through contents of files

• grep [options] <searchstring>
  Examples:
  • grep -i diffeomorphism *.tex: case-insensitive search
  • grep -w diffeomorphism *.tex: match word boundaries, i.e. a line with diffeomorphisms but not diffeomorphism won't be printed.
  • grep -l diffeomorphism *.tex: show only the names of the files with desired contents, but don't show all the lines themselves.

Determining file types

• file [options] filename

Viewing text files

• cat [options] filename — to display the file contents without pause or break.
• less [options] filename — to display file contents page by page.
• more [options] filename — to display file contents page by page.
• head [options] filename — to display the first few lines of a file.
  Example: head -20 thesis.tex shows the first 20 lines of thesis.tex.
• tail [options] filename — to display the last few lines of a file.
  Example: tail -20 thesis.tex shows the last 20 lines of thesis.tex.

Editing text files

• To edit a text file type: editorname filename [&], where editorname could be one of the following: GNU-emacs, vi, joe, pico, etc. (note: change these links to the internal editor site)

Compressing and decompressing files

Reading compressed text files

• zless [options] compressedfilename — to display the contents page by page without uncompressing the file.

Archiving (packaging) files and directories

• tar [options] filenamelist archive.tar — to archive files (store and extract). Compression and decompression is available in the following formats: .bz2(.bz) or .gz.
  Examples:
  • tar zcf rtg_project.tgz rtg_project: package up the directory called rtg_project, putting a copy of everything into the compressed tar file rtg_project.tgz. Now you can put this file on a thumb drive, e-mail it to someone across the country, etc. etc. The c is for create.
  • tar ztf rtg_project.tgz: List out the contents of the compressed tar file rtg_project.tgz, just to see what's in it. The t is for table of contents.
  • tar zxf rtg_project.tgz: Extract the contents of the compressed tar file rtg_project.tgz. Warning: this may overwrite existing files with the same name, if any are present. The x is for extract.
• cpio [options] filenamelist — to copy files to and from an archive.
• zip / unzip [options] archivename.zip filenamelist — to package and unpackeage compressed archives.
• zoo [options] archive filename — to create and maintain collections of files in compressed form.

Managing print jobs

• lpr [options] filenames... — to print files.
• lpq [options] — to check printer que status.
• lprm [options] printjobIDs — to cancel print jobs.

Using floppy diskettes and CD-ROMs

• mount /mnt/floppy — to mount floppies.
• mount /mnt/cdrom — to mount CD-ROMs.
• umount /mnt/floppy — to unmount floppies.
• umount /mnt/cdrom — to unmount CD-ROMs.
• mkisofs [options] filename [specifications] — to create a binary ISO image file.
• cdrecord [options] tracks... — to record audio or data compact discs.
• mtools — alternative file manipulation commands for DOS disks. Instead of mounting a disk, with the mount command as above, and using standard Linux commands like cp, ls, mv, etc. one can use the mtool commands to manipulate files. Consult man mtools for information about these commands.

Remote access

• ssh [options] user[@host] — to make secure shell connections.
  Example: ssh -X rlakatos@gila.math.arizona.edu. The -X option allows you to run graphical-interface programs, as long as you're ssh'ing from a Un*x-like machine (e.g. another Linux machine).
• scp [options] [user1@host1]:filenames... user2@host2:filenames... — to securely copy individual files.
  Examples:
  • scp myfile.txt rlakatos@gila.math.arizona.edu:tmp:
  Copy myfile.txt on the current machine to ~/tmp on host gila.
  • scp myfile.txt rlakatos@gila.math.arizona.edu:/tmp:
  Copy myfile.txt on the current machine to /tmp on host gila.
  • scp rlakatos@gila.math.arizona.edu:/tmp/myfile.txt .:
  Copy myfile.txt on host gila to the current machine.
• sftp [options] [user]@host — to start a powerful interactive secure file transfer program.

Running applications in the background

• nohup commandname [arguments] — to run a command, with a non-tty output, that should continue running after exiting the prompt.
• nice [options] commandname [arguments] — to run a program with modified scheduling priority.
• renice priority [options] — to alter the priority of a running process.
• & — to put a job in the background (for example emacs mytext.txt &).
• bg [jobspec] — to resume the suspended job jobspec in the background as if it had been started with &.
• fg [jobspec] — to put the specified job in the foreground (to make it the current job).

Processes and disk space

• ps [options] — to display active proccesses.
• kill [options] processID — to send a signal to a process ("kill" is a misnomer).
• top [options] — to display top CPU processes.
• free [options] — to display information about free and used memory on the system.
• df [options] file(system)name — to get information on filesystem disk space usage.
• du [options]filename — to estimate file space usage.
  Example: du -s ~/* ~/.* | sort -r: find which subdirectories of your home directory are using up the most space.

Command-line history, I/O redirection, and piping

• history [options] — to display the command line history.
• <tab> key — to complete a partially typed file/directory name or command.
• <↑> / <↓> keys — to navigate the command history buffer.
• ; — to separate multiple commands on a single line. For example command1 ; command2.
• >,>> — to redirect the output of a command. For example ls -la directoryname > myfile.txt will write the output of the ls command to the file myfile.txt (and not to the screen!) while overwriting any previous contents of the file. If >> is used instead of > the original contents of the file myfile.txt will not be ereased but the output of ls will be appended to it.
• < — to use a specific file as an input to a command. For example cpio [options] < filenamelistfile.txt
• | — to pipe the output of one command to another command. For example ls -al directoryname | less.

Miscellaneous

• date [options] — to display and set the system date and time.
• clear — to clear the terminal window.
• reset [options] — to reset the terminal window to its default display settings.

Starting applications

• To launch an application from a shell prompt simply type the name of the application at the prompt.

Viewer applications

Converting between document formats

• Click here for TeX usage diagram.

Image manipulation from a shell prompt

There are programs for manipulating image files that can be run at a shell prompt without a need for a graphical interface like the one that the gimp application uses. These programs are known under the collective name Netpbm which also stands for a collection of image formats (also known as npm formats) that can be used as intermediary formats for converting bettwen the most popular standard image types (e.g. .jpeg, .png). These formats have extensions like .ppm which stands for portable pixmap, .pgm for portable graymap, and .pbm for portable bitmaps. To learn more about these commands, check out this link or visit the manual or info pages for the jpegtopnm command.