Selected Linux commands

Tips & first steps

Command-line tricks:

• Type Control-R and start typing = will match last command that started that way
• Tab will autocomplete everything, but from all available commands

Most useful to quickly locate commands, executable is "locate", such as:

 locate memcached # or
 whereis memcached
 apropos ftp # searches for all ftp programs

Traditional find files uses:

 find / -name 'file.ext' # "/" to start at root, option -name to search for file names

Very useful to find software which may not yet be installed:

 apt-cache search YourSearchTerm

Get help

 apropos ftp # searches for all program descriptions with ftp
 man 7z # manual page for 7z
   # shift + ? → searching a string (by regular expression)
   # shift + n/n → find the next/previous match
   # q → quit

Most commands provide a help option and the following works:

 a-command --help
 a-command -h
 # sometimes there is an info on usage
 a-command --usage

Stop services / demons

 /etc/init.d/apache2 stop
 /etc/init.d/memcached stop
 /etc/init.d/mysql stop
 /etc/init.d/tomcat5.5 stop
 /etc/init.d/webmin stop

to restart (template to copy and use directly):

 /etc/init.d/apache2 start
 # /etc/init.d/memcached start
 /etc/init.d/mysql start
 /etc/init.d/tomcat5.5 start
 /etc/init.d/webmin start

Fedora may or may not be installed under the main tomcat. As of 2009-08, it can be started/stopped using (fedora folder is a softlink to current installed version; alternatively one can use "$FEDORA_HOME"):

 /usr/share/fedora/tomcat/bin/shutdown.sh
 /usr/share/fedora/tomcat/bin/startup.sh

Disk usage and rights

How much space on disks?

 df -l # diskfree, local disks only
 df -lh # diskfree, human friendly (size in MB, GB, etc.)
 df .  # diskfree current disk

Disk usage = "tree size": where is the space used:

 du -h --max-depth=1 # '''analyze only 1 level of directories deep'''
     # -h = human readable, MB, GB, factor 1024; -si would be factor 1000.
 du -S # do not add up content of folders, keep values Separate (useful for manual analysis)

For rights, it is often necessary to change the group of a file or folder. It is not necessary to change the owner as well (chown -R).

 ls -l    # will display owner and group names
 ls -g    # will only display group names (easier)
 chgrp -R # R: do it recursively

When copying folder trees, it is easy to loose essential information. Use

 cp -pr  # preserve owner, rights, etc., copy recursively; 
 # but devices, sockets, etc. still are not handled, if this is necessary use:
 tar -p

Searching

Locate does not work, and using Find is tough. Good info: http://content.hccfl.edu/pollock/unix/findcmd.htm Example for find:

  find / -name index.html

For searching inside files, use grep (-r searches recursive, but only within the file pattern, grep -r "x" index.html would not work!):

 grep -r "<script>" *

Other commands

• less to read, tail to read end of log file, nano: an easier editor on debian 4 with syntax highlighting set globally in /etc/nanorc.
• ls -lap to better see all files, a for hidden, p to see folders marked with trailing "/"

• cat /etc/passwd to see user list, cat = list, here: the password file
• cat -v filename to display non-printing characters so they are visible. If the file has been edited on a Windows machine it can sometimes add CR/LF (VM) characters on the end of each line (hidden by default on most editors), so #!/bin/sh becomes #!/bin/shVM. This causes error: bad interpreter ^M. To remove such characters, use e.g. cat infilename | tr -d "\r" > outfilename
• adduser, deluser, passwd more on user management: http://www.cae.wisc.edu/site/public/?title=linaccounts
• "taskmanager": ps -ef list all processes, including services, use kill (number) or pkill (name)
• "taskmanager" interactive: top or top u root list all processes; u switches the user; Shift+F change sorting column; > or < switches sorting to → or ←; Shift+R alters descending or ascending column sorting; k kill; c show command paths instead of process names; q quit
• kill processes by name: for example killall memcached

vnc = special vnc user, not sure whether useful.

A source helping to understand the Linux file system is: http://www.pathname.com/fhs/pub/fhs-2.3.html

Install commands

• To find package names use:
  • aptitude search (keyword)
  • apt-cache search (keyword)
• Clean-up:
  • apt-get autoremove will remove packages no longer needed.
  • apt-get clean will clear the repository completely

• dpkg -l to list all packages with codes for status, e.g.'ii' for installed,'rc' for removed, but configuration files still there; dpkg -s (package name) to get information on the status of a package

ls colors

Putty displays ls out in colors. These are:

• Executable files: Green
• Normal file : Normal
• Directory: Blue
• Symbolic link : Cyan
• Pipe: Yellow
• Socket: Magenta
• Block device driver: Bold yellow foreground, with black background
• Character device driver: Bold yellow foreground, with black background
• Orphaned syminks : Blinking Bold white with red background
• Missing links ( - and the files they point to) : Blinking Bold white with red background
• Archives or compressed : Red (.tar, .gz, .zip, .rpm)
• Image files : Magenta (.jpg, gif, bmp, png, tif)

OR (other source):

Type                Foreground Background
Folder/Directory    blue      (default)
Symlink             magenta   (default)
Socket              green     (default)
Pipe                brown     (default)
Executable          red       (default)
Block               blue      cyan
Character           blue      brown
Exec. w/ SUID       black     red
Exec. w/ SGID       black     cyan
Dir, o+w, sticky    black     green
Dir, o+w, unsticky  black     brown

Renaming file extensions

Linux does not support wildcards in the target of a move command the way Windows does. The equivalent for Windows:

rename *.jpeg *.jpg

is

for files in *.jpeg; 
   do n=${files/.jpeg/.jpg}; # saves to variable $n
   mv $files $n; 
done

Related: To add a prefix use:

 for i in *.jpg; do mv -i "$i" "XXX_$i"; done

Archiving

With the general zip, p7zip-full etc. installed, the following commands work:

 # -9 is optional, higher compression
 zip archivename.zip file.sql /folder -9  
 unzip archivename.zip
 # for real good compression use:
 # (a = add, -mx7 and -mx9 = higher compression, x = extract)
 7z a archivename.7z file.sql /folder
 7z x archivename.7z

Note: Because 7z will not store owner or group information, the option -r = recurse into subfolders is not recommended. To archive folders use (where ! is the folder name, as in WinSCP custom commands):

 # tar + 7z a folder: cf = create file, a = add, -si = Read data from StdIn
 tar cf - "!" | 7za a -si -mx7 "!.tar.7z"
 # tar/7z to folder: x = eXtract with full paths, -so = Write data to StdOut, bd = Disable percentage indicator
 # xf = extract file
 7za x -so -bd "!" | tar xf -

Note: inside WinSCP, the tar/7z command to folder results in error (ok in ssh), but simply selecting SKIP results in correct result, this seems to be more a bug of the way WinSCP handles messages than of the process (?).