UNIX System administration PHẦN 1 ppsx

Basics of the UNIX command line I don’t give full details of these commands, just the most useful options.. Finding files: find Simplified syntax: find startdirectory -name filename -pri

UNIX: System administration

A Concise Guide

By Rudolf Cardinal

Revision dated 18th August 1995

INTRODUCTION 7

Commands preceded by a colon (ed commands) 12

Filenames and Wildcards 15

MANAGING PROCESSES SNOOPING AND KILLING ERRANT TASKS 24

Swapping out 25

The lpstat command – printer status information 40

The lpc command – line printer control 41

LANs and beyond: address resolution, routing and complex services 49

Some important client programs for users and administrators 63

What is a shell? 73

The ULTRIX manuals and their abbreviations 87

This is a guide for system administrators It assumes reasonable familiarity with syntactic definitions and command-line operating systems in general, and some skill with the basics of UNIX (cataloguing disks, editing files and so forth) It also assumes you have full authority over your system I don’t usually mention when superuser authority is required for a particular command: in general, anything that affects other users, their processes or their data requires root authority

I have based this guide on ULTRIX from Digital; this is a BSD UNIX clone

This is primarily a reference guide, to look things up in and not to read from cover to cover

What is UNIX?

UNIX is a multiuser operating system It is organised into a kernel, the main “program” that is the operating system, and a set of utility programs found on disk It provides facilities for many users to run programs simultaneously, and to keep files on the system, with no impact on each other aside from the system’s apparent speed In order to administer UNIX there is a superuser, “root”, with complete authority over all aspects of the system That’s you, that is

Basics of the UNIX command line

I don’t give full details of these commands, just the most useful options See Getting Help for details

of the manuals

Finding files: find

Simplified syntax:

find startdirectory -name filename -print

Without the -print command, you don’t see the result

Examples:

find / -name rc.local -print

find /usr -name ’*.c’ -print

Examining a directory: ls

ls -al Full details

ls filespec About a given file/group of files

ls -al | grep ’^d’ List all directories

Deleting, copying and renaming files

rm filename Deletes

cp source dest Copies The -r option allows recursive copying

mv source dest Moves or renames See mv(1)

These can take the parameters – (“everything that follows is a filename”, so you can use filenames starting with -); -f (force); -i (interactive mode) and -r (recurse subdirectories) The mv command cannot take -r The cp command can also take -p (preserve file dates/times/modes) Possibly the worst thing you can do to UNIX is to issue the command “rm -r *” from the root directory while you are superuser

Creating and deleting directories

mkdir directory Makes a directory

rmdir directory Removes a directory

Moving around directories

cd [ directory ] Change to directory If no directory is specified, the directory specified

in the environment variable $HOME (the user’s home directory) is used instead

pwd Print working directory

Viewing and editing files

cat filename Same as type in DOS

more filename Same as more in DOS; equivalent to cat filename | more, which

also works Also equivalent to more < filename Space for next page,

q to quit If you use more as “more filename”, you can also press b to move back a page; the other forms of the command use piped input and b doesn’t work

head filename Looks at the top of a file Can use as in head –30 filename, to look

at the top 30 lines

tail filename Looks at the end of a file Can specify line count as for head

Pattern searching: grep

grep stands for “get regular expression” grep can be used, like more, as a filter (command | grep options), a place to route input (grep options < file) or as a straight command (grep

options file).

Syntax:

grep [ options ] expression [ file ]

When specifying a pattern (“expression”) to match, there are many special characters and wildcards: see grep(1) for details of these and all the other options The following patterns are the most useful:

^ beginning of a line

$ end of a line

any character normal character that character

[string] any character from string; you can use ranges as in [a-z0-9]

* zero or more characters Examples:

ls -al | grep ’^d’ Catalogues all directories in the current directory by

searching for lines in the output of “ls -al” that begin with a d

grep fish tree.c Looks for the word “fish” in the file tree.c

grep execute *.h Looks for “execute” in all files ending “.h” If

more than one file satisfies this criterion, its name will be shown in the output from grep so you know where to look

grep fish < tree.c Same as “grep fish tree.c”

ps -aux | grep ’^oracle’ | more Gives process status information on all processes

owned by oracle, pausing between pages

For more complex pattern-matching, use egrep(1) or fgrep(1).

Editing files: a brief guide to vi

Fire it up with vi filename.

For read-only access, use view filename.

Pronounced “vee-eye”, vi exists in two states: edit mode and command mode You begin in command mode At any time, you can return to command mode by pressing Escape (If you’re on a

VT terminal and you get a back quote, you can either go into the terminal’s keyboard setup and make that key send ESC, or you can use Ctrl-[ instead of Escape Escape and Ctrl-[ both send character number 27, which is what you’re after.) If you were in command mode anyway, it beeps at you Now for some commands – note that these are all case-sensitive! By the way, ^X is a convention for Ctrl-X

Cursor movement

SPACE Advance the cursor one position

^B Move backward a page (A count specifies repetition.)

^D Scrolls down (A count specifies number of lines and is remembered for future ^D and

^U commands Default is a half-page.)

^E Exposes another line at the bottom

^F Move forward a page (A count specifies repetition.)

^H Backspace the cursor

^J Move cursor down (same as down arrow)

^M A carriage return advances to the next line at the first non-white character Given a

count, it advances that many lines (as in 5^M) During an insert, it causes the insert to continue onto another line

^N Next line, same column (same as down arrow)

^P Previous line, same column (same as up arrow)

^U Scrolls up (see ^D)

^Y Exposes another line at the top

0 Go to start of line

^ First non-white on line

% Finds matching bracket, brace or box Useful for programming!

) Forward sentence

} Forward paragraph

]] Forward section

( Backward sentence

{ Backward paragraph

[[ Backward section

+ Next line, at the beginning

– Previous line, at the beginning

/ Scan for a string (that follows the / ), forwards

? Scan backwards

B Back a word, ignoring punctuation

H Home screen line

M Middle screen line

<line> G Go to a particular line So 1G goes to the top of the document; 100G goes to line

100 If you type G on its own, you go to the end of the file.

L Last screen line

W Forward a word, ignoring punctuation

b Back a word

e End of current word

h Move left