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lsof command and options

lsof - list open files. An  open file may be a regular file, a directory, a block special file, a character special file, an executing text reference, a library, a stream or a network file (Internet socket, NFS file or UNIX domain socket.)  A specific file or all the files in a file system may be selected by path. Given that this command identifies which files are being used, this information can be used when disk can not be unmounted due to files being used or opened.
Type the following command:
$lsof
    lsof.png
Herein -
FD – stands for File descriptor and may have some of the values as:
  1. cwd current working directory
  2. rtd root directory
  3. txt program text (code and data)
  4. mem memory-mapped file
Also in FD column numbers like 41u is actual file descriptor and followed by u,r,w of it’s mode as:
  1. r for read access.
  2. w for write access.
  3. u for read and write access.
TYPE – of files and it’s identification.
  1. DIR – Directory
  2. REG – Regular file
  3. CHR – Character special file.
  4. FIFO – First In First Out
  5. IPv4
  6. IPv6
OPTIONS
-u s selects the listing of files for the user whose login names or user ID numbers are in the comma-separated set s -  e.g.,  ``abe'', or ``548,root''.  (There should be no spaces in the set.)
    $lsof -u tarun
-i [i] selects the listing of files any of whose Internet address matches the address specified in i. If no address is specified, this option selects the listing of all Internet and x.25 (HP-UX) network files. Following command lists all network connections listening and established -
$lsof -i
Screenshot from 2015-07-22 14:35:31.png
An Internet address is specified in the form (Items in square brackets are optional.):
[46][protocol][@hostname|hostaddr][:service|port]
    $lsof -i TCP:80
Screenshot from 2015-07-22 14:13:46.png
List running processes of open files of TCP port range from 1-800
    $lsof -i TCP:1-800
Screenshot from 2015-07-22 14:25:27.png
If -i4 or -i6 is specified with no following address, only files of the indicated IP version, IPv4 or IPv6,  are  displayed.
    $lsof -i4
    Screenshot from 2015-07-22 14:22:02.png
    $lsof -i6
Screenshot from 2015-07-22 14:22:30.png

-p s excludes or selects the listing of files for the processes  whose  optional  process  IDentification  (PID)  numbers  are  in  the comma-separated set s - e.g., ``123'' or ``123,^456''.  (There should be no spaces in the set.) PID numbers that begin with `^' (negation) represent exclusions.

        $lsof -p 2499

-t   specifies  that  lsof  should  produce  terse output with process identifiers only and no header - e.g., so that the output may be piped to kill(1)

        $lsof -p 2499

        $kill -9 `lspf -t -u tarun`

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