Monday, January 5, 2015

Usefull linux commands

  • find folderABC -mtime -9 -- show files in and below folder ABC modified less than 9 days ago
  • ps
    • ps aux | grep myprocesspartialname - not no '-' before the options
    • /bin/ps -context -www -p processID -- shows wide command line for the process
  • svn status | grep '^M' -- shows files modified in the current SVN copy
  • svn diff -r HEAD fileABC -- compares the file ABC to its most recent version in the repo
  • zip+unzip:
    • unzip zip-file -d destination-folder  -- unzip a file
  • tar+gzip:
    • tar -ztvf file.tar.gz -- list contents of gzipped tar archive file.tar.gz
    • tar -czf file.tar.gz file1 file2 file3 -- create a gzipped archive file.tar.gz with three files in it
    • tar -xzf tar-file-name.tar.gz
  • bzip2
    • to unpack a bz2 file use command:  bzip2 -dk filename.bz2
  •  vim:
    • search - just like in vi, by hitting / you can search by specifying a regex pattern
    • to search for a whole word: \<...\>
    • to escape a special char, for example to search for a path, do: \/opt\/jboss
    • to cut lines into a vim internal clipboard, use dd command.
    • option :set-nowrap turns of the default, and sometimes annoying, line wrapping
    • to toggle word wrapping, use command:  :set wrap!
    • to do case-ignore search do /\cAlicja, and to do case sensitive search use \C
    • to mark a location type m L, where L is any letter, e.g. m a, and to move back to this location type: ' L (single apostrophe)
    • to place the current line at the top, center or bottom, hit zt, z., or zb.
  •  symbolic link: ln -s target link-name
    To me, it seems backward, but I guess you can say it like this: take target and call it link-name 
  •  folders
    •  remove: rm -r folder-name
      (note: rmdir will delete only an empty folder)
    • copy: cp -r folder-name dest-folder-name
    •  with -f option, you can avoid any questions 
    • by convention: folder/* means contents of the folder, while folder/ means all of the folder 
  • diff files and folders
    •  -wBb file1 file2 -- diff two files with all whitespaces ignored (new lines are not ignored-this is a much more complex problen, even just conceptually) 
    • -r dir1 ird2 -- recursively, shows files found only in one of the trees, for binaries shows message "files different"
  • du which tells "how much of the precious space does a this folder or files use":
    • du -sh my-folder/*  -- shows size of all files and folders in my-folder folder, one number per file/folder
  • df -h  which shows you the list of the files systems and which of them full if any.
  • grep
    •  ignoring the useless Permission denied entries.  Can be done using a redirection: grep my-cat-Lois my-folder/Lois-files 2> /dev/null
    • with a regex.  The simplest regex to find one or more tabs in the file was:
      grep '^This[[:space:]]\+5' parms*.txt
    • to show only the file names, use option -l
    • to search through compressed .bz2 files, use bzgrep instead of grep
    • to search for words, use option -w
  • su and sudo  -- both can take a user as a parm (superuser by default).  The su switches to that user until you do exit, while sudo is followed by a command, that only this one command is executed in the assumed user context.  
  • chown -R jboss:jboss_grp * --  change ownership of all files in this folder and below to user jboss, group jboss_grp.
  • adduser username -- add a new user and add user to the group. Once the user is created, to add user to the sudo group, repeat the same command with one more argument at the end: sudo
  • usermod -a -G sudo jdoe  -- add user to group sudo
  • passwd user1 -- change password for user1. Use option -e to have force user to change it at the first login.
  • awk -F '\t' ' /^Product\t/ {print $7} ' file.txt 
    • -F - Tab as a separator (deault: spc)
    • '...'  - program, inline  
    • default program structure: condition action
    •  Together: above command prints 7th (tab-separated) element of all lines of file file.txt that start with 'Product\TAB'
    • a bit more complex script:  { if( $0 ~ /^Fund\t/ && $10 == "False") {print $13} } -- It prints 13th element of the record, but only for lines starting with 'Fund', where the element 10th is 'False'.
    • and, if you need to process mutliple files, one option is a shell script:
      #!/bin/bash
      for var in $(ls /var/GOLL/import/exportPP_*.txt); do
        ls -l $var
        awk -F '\t' ' { if( $0 ~ /^Fund\t/ && $10 == "True") {print $3, $6, "ClosedDate:", $8, $10, $11, $12, $13} }' $var
      done
  • dmsg  show system messages, e.g. out-of-memory errors and processes killed as a result
  • working in command line:
    • to find a previous command you can use Ctrl-R (reverse search) 
  • less, tail and vim - you can open a file to view anypart of it using vim-like commands and switch to the 'tail -f' mode with Ctrl-F.  Then, Ctrl-C will take you back to viewing the whole file.
  • mkdir -p /var/dir1/dir2  -- create directory with all its missing parents
  • getfacl folder  -- show details of custome access specs for a folder (it shows as + on the long directory/file listing)
  • cat /etc/*release  -- show the name and version of the OS

Groups

  • groups [user]  -- show groups that user belongs to (by default - this user)
  • groupadd grouptoadd  -- creates a new group
  • cat /etc/group  -- shows one line per group with all its members; grep the list as needed
  • gpasswd -a user group  -- adds user to the group (-d for delete from the group)

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