LPI Linux Certification in a Nutshell (39 page)

• Processes have:
  

  • A lifetime
    

  • A PID
    

  • A UID
    

  • A GID
    

  • A parent process
    

  • An environment
    

  • A current working directory
    

ps

Generate a one-time snapshot of the current processes on
standard output.

pstree

Display a hierarchical list of processes in a tree
format.

top

Generate a continuous, formatted, real-time process
activity display on a terminal or in a terminal window.

• Processes listen for
  signals
  sent by the kernel or users using the
  kill
  command:
  

  kill
  -
  sigspec
  [
  pids
  ]
  

  Send
  sigspec
to
  pids
.
  

• The
  killall
  command is used to send
  signals to processes by program name instead of PID.
  

• Common
  kill
  signals are listed in
  Table 10-6
  .
  

Table 10-6. Common signals

HUP

INT

KILL

TERM

TSTP

bg
[
jobspec
]

Place
jobspec
in the background
as if it had been started with
&
.

fg
[
jobspec
]

Place
jobspec
in the
foreground, making it the current job.

jobs
[
jobspecs
]

List
jobspecs
on standard
output.

nohup
[
command
] &

Execute
command
, detach it from
the terminal, and allow it to continue running after the user
logs out.

• A process’s
  execution priority
  is managed by the kernel.
  

• You can bias the execution priority by specifying a
  nice number
  in the range of –20 to +19
  (default is 0).
  

• Positive nice numbers reduce priority; negative nice numbers
  increase priority and are reserved for the superuser.
  

nice
-
adjustment
[
command
]

Apply nice number
adjustment
to
the process created to run
command
.

renice
[+|-]
nicenumber
targets


Alter the
nicenumber
, and thus
the scheduling priority, of one or more running
target
processes.

• Regular expressions
  are used to
  match text. The term is used to describe the loosely defined
  text-matching language as well as the patterns themselves. A
  regular expression is often called a
  regex
  or
  a
  regexp
  .
  

• Regular expressions are made up of
  metacharacters
  (with special
  meaning) and
  literals
  (everything that is not
  a metacharacter).
  

• The backslash character (
  \
) turns off (escapes) the special
  meaning of the character that follows, turning metacharacters into
  literals. For nonmetacharacters, it often turns on some special
  meaning.
  

Table 10-7. Regular expression position anchors

^

$

\<

\>

Table 10-8. Regular expression character sets

[
abc
]

[
a-z
]

[^
abc
]

[^
a-z
]

.

Table 10-9. Regular expression modifiers

*

*

\?

?

\+

+

\{
n
,
m
\}

{
n
,
m
}

\|

|

\(
regex
\)

(
regex
)

• Many commands support the regular expression syntax, but the
  most commonly used is the command
  grep
  , which
  is designed to display lines from a file or files matching a given
  regular expression.
  

• There are multiple ways to call
  grep
  to
  change its behavior:
  

  grep
  

  Treat the pattern as a basic regular
  expression.
  

  egrep
  

  Treat the pattern as an extended regular expression.
  Same as
  grep –E
  .
  

  fgrep
  

  Treat the pattern as a list of fixed strings, any of
  which may be matched. Same as
  grep
  –F
  .
  

• Start
  vi
  with
  vi
  file1
[
  file2
[...]]
  . See
  Table 10-10
  .
  

  Table 10-10. Basic vi editing commands
  

  Command	Description
  Esc	Exit insert mode and put the editor into command mode.
  h or left arrow	Move left one character.
  j or down arrow	Move down one line.
  k or up arrow	Move up one line.
  l or right arrow	Move right one character.
  H	Move to the top of the screen.
  L	Move to the bottom of the screen.
  G	Move to the end of the file.
  W	Move forward one word.
  B	Move backward one word.
  0 (zero)	Move to the beginning of the current line.
  ^	Move to the first nonwhitespace character on the current line.
  $	Move to the end of the current line.
  Ctrl-B	Move up (back) one screen.
  Ctrl-F	Move down (forward) one screen.
  i	Insert at the current cursor position.
  I	Insert at the beginning of the current line.
  a	Append after the current cursor position.
  A	Append to the end of the current line.
  o	Start a new line after the current line.
  O	Start a new line before the current line.
  r	Replace the character at the current cursor position.
  R	Start replacing (overwriting) at the current cursor position.
  x	Delete the character at the current cursor position.
  X	Delete the character immediately before (to the left) of the current cursor position.
  s	Delete the character at the current cursor position and go into insert mode. (This is the equivalent of the combination xi .)
  S	Delete the contents of the current line and go into insert mode.
  d X	Given a movement command X , cut (delete) the appropriate number of characters, words, or lines from the current cursor position.
  dd	Cut the entire current line.
  D	Cut from the current cursor position to the end of the line. (This is equivalent to d$ .)
  c X	Given a movement command X , cut the appropriate number of characters, words, or lines from the current cursor position and go into insert mode.
  cc	Cut the entire current line and go into insert mode.
  C	Cut from the current cursor position to the end of the line and enter insert mode. (This is equivalent to c$ .)
  y X	Given a movement command X , copy (yank) the appropriate number of characters, words, or lines from the current cursor position.
  yy or Y	Copy the entire current line.
  p	Paste after the current cursor position.
  P	Paste before the current cursor position.
  .	Repeat the last command.
  u	Undo the last command.
  / regex	Search forward for regex .
  ? regex	Search backward for regex .
  n	Find the next match.
  N	Find the previous match. (In other words, repeat the last search in the opposite direction.)
  :n	Next file; when multiple files are specified for editing, this command loads the next file. Force this action (if the current file has unsaved changes) with :n! .
  :e file	Load file in place of the current file. Force this action with :e! file .
  :r file	Insert the contents of file after the current cursor position.
  :q	Quit without saving changes. Force this action with :q! .
  :w file	Write the current buffer to file . To append to an existing file, use :w >> file . Force the write (when possible, such as when running as root) with :w! file .
  :wq	Write the file contents and quit. Force this action with :wq! .
  :x	Write the file contents (if changed) and quit (the ex equivalent of ZZ ).
  ZZ	Write the file contents (if changed) and quit.
  :! command	Execute command in a subshell.