Unix Commands Part 2 by MuthuKumar.v


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									                                 Unix commands
                               File                comparison and             Text
Misc commands
                               management          searching                  processing
Shell and other
                               communications Storage commands                System status
                                 Misc commands
man,banner,cal, calendar,clear,nohup, tty .

Man ual command.
man man This is help command, and will explains you about online manual pages you
can also use man in conjunction with any command to learn more about that command
for example.

      man ls will explain about the ls command and how you can use it.
      man -k pattern command will search for the pattern in given command.

Banner command.
banner prints characters in a sort of ascii art poster, for example to print wait in big
letters. I will type
banner wait at unix command line or in my script. This is how it will look.

 #    #          ##       #       #####
 #    #      #        #   #         #
 #    #    #    #         #         #
 # ## #    ######         #         #
 ## ##     #    #         #         #
 #    #    #    #         #         #

Cal command
cal command will print the calander on current month by default. If you want to print
calander of august of 1965. That's eightht month of 1965.
cal 8 1965 will print following results.

    August 1965
 S M Tu W Th F S
 1 2 3 4 5 6 7
 8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

Clear command
clear command clears the screen and puts cursor at beginning of first line.

Calendar command
calendar command reads your calendar file and displays only lines with current day.
For example in your calendar file if you have this

12/20     Test new software.
1/15      Test newly developed 3270 product.
1/20      Install memory on HP 9000 machine.
On dec 20th the first line will be displayed. you can use this command with your crontab
file or in your login files.

Nohup command.
nohup command if added in front of any command will continue running the command or
process even if you shut down your terminal or close your session to machine. For
exmaple, if I want to run a job that takes lot of time and must be run from terminal and is
called update_entries_tonight .
nohup update_entries_tonight will run the job even if terminal is shut down in middle of
this job.

Tty command
Tty command will display your terminal. Syntax is
tty options


       -l will print the synchronous line number.
       -s will return only the codes: 0 (a terminal), 1 (not a terminal), 2 (invalid options)
        (good for scripts)
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                      File Management commands.
cat,cd, cp, file,head,tail, ln,ls,mkdir ,more,mv, pwd, rcp,rm, rmdir, wc.

Pwd command.
pwd command will print your home directory on screen, pwd means print working

is output for the command when I use pwd in /u0/ssb/sandeep directory.

Ls command
ls command is most widely used command and it displays the contents of directory.


      ls will list all the files in your home directory, this command has many options.
      ls -l will list all the file names, permissions, group, etc in long format.
      ls -a will list all the files including hidden files that start with . .
      ls -lt will list all files names based on the time of creation, newer files bring first.
      ls -Fxwill list files and directory names will be followed by slash.
      ls -Rwill lists all the files and files in the all the directories, recursively.
      ls -R | more will list all the files and files in all the directories, one page at a time.

Mkdir command.
mkdir sandeep will create new directory, i.e. here sandeep directory is created.

Cd command.
cd sandeep will change directory from current directory to sandeep directory.
Use pwd to check your current directory and ls to see if sandeep directory is there or not.
You can then use cd sandeep to change the directory to this new directory.
Cat command
cat cal.txt cat command displays the contents of a file here cal.txt on screen (or standard

Head command.
head filename by default will display the first 10 lines of a file.
If you want first 50 lines you can use head -50 filename or for 37 lines head -37 filename
and so forth.

Tail command.
tail filename by default will display the last 10 lines of a file.
If you want last 50 lines then you can use tail -50 filename.

More command. more command will display a page at a time and then wait for input
which is spacebar. For example if you have a file which is 500 lines and you want to read
it all. So you can use

more filename

Wc command
wc command counts the characters, words or lines in a file depending upon the option.


       wc -l filename will print total number of lines in a file.
       wc -w filename will print total number of words in a file.
       wc -c filename will print total number of characters in a file.

File command.
File command displays about the contents of a given file, whether it is a text (Ascii) or
binary file. To use it type
file filename. For example I have cal.txt which has ascii characters about calander of
current month and I have resume1.doc file which is a binariy file in microsoft word. I will
file resume.doc
resume1.doc:         data
file cal.txt
cal.txt:             ascii text

Cp command.
cp command copies a file. If I want to copy a file named oldfile in a current directory to a
file named newfile in a current directory.
cp oldfile newfile
If I want to copy oldfile to other directory for example /tmp then
cp oldfile /tmp/newfile. Useful options available with cp are -p and -r . -p options
preserves the modification time and permissions, -r recursively copy a directory and its
files, duplicating the tree structure.

Rcp command.
rcp command will copy files between two unix systems and works just like cp command
(-p and -i options too).
For example you are on a unix system that is called Cheetah and want to copy a file
which is in current directory to a system that is called lion in /usr/john/ directory then you
can use rcp command
rcp filename lion:/usr/john
You will also need permissions between the two machines. For more infor type man rcp
at command line.

Mv command.
mv command is used to move a file from one directory to another directory or to rename
a file.

        Some examples:

       mv oldfile newfile will rename oldfile to newfile.
       mv -i oldfile newfile for confirmation prompt.
       mv -f oldfile newfile will force the rename even if target file exists.
       mv * /usr/bajwa/ will move all the files in current directory to /usr/bajwa

Ln command.
Instead of copying you can also make links to existing files using ln command.
If you want to create a link to a file called coolfile in /usr/local/bin directory then you can
enter this command.
ln mycoolfile /usr/local/bin/coolfile

       Some examples:

      ln -s fileone filetwo will create a symbolic link and can exist across machines.
      ln -n option will not overwrite existing files.
      ln -f will force the link to occur.

Rm command.
To delete files use rm command.


      rm oldfile will delete file named oldfile.
      rm -f option will remove write-protected files without prompting.
      rm -r option will delete the entire directory as well as all the subdirectories, very
       dangerous command.

Rmdir command.
rmdir command will remove directory or directories if a directory is empty.


      rm -r directory_name will remove all files even if directory is not empty.
      rmdir sandeep is how you use it to remove sandeep directory.
      rmdir -p will remove directories and any parent directories that are empty.
      rmdir -s will suppress standard error messages caused by -p.

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                        Comparison and Searching
diff,dircmp, cmp, grep, find.
Diff command.
diff command will compare the two files and print out the differences between.
Here I have two ascii text files. fileone and file two.
Contents of fileone are

This   is   first file
this   is   second line
this   is   third line
this   is   different     as;lkdjf
this   is   not different

filetwo contains
This   is   first file
this   is   second line
this   is   third line
this   is   different     xxxxxxxas;lkdjf
this   is   not different

diff fileone filetwo will give following output
< this is different           as;lkdjf
> this is different           xxxxxxxas;lkdjf

Cmp command.
cmp command compares the two files. For exmaple I have two different files fileone and
cmp fileone filetwo will give me

fileone filetwo differ: char 80, line 4

if I run cmp command on similar files nothing is returned.
-s command can be used to return exit codes. i.e. return 0 if files are identical, 1 if files
are different, 2 if files are inaccessible.
This following command prints a message 'no changes' if files are same
cmp -s fileone file1 && echo 'no changes' .
no changes

Dircmp Command.
dircmp command compares two directories. If i have two directories in my home
directory named
dirone and dirtwo and each has 5-10 files in it. Then
dircmp dirone dirtwo will return this

 Dec    9 16:06 1997      dirone only and dirtwo only Page 1
./cal.txt                                                ./fourth.txt
./dohazaar.txt                                           ./rmt.txt
./four.txt                                               ./te.txt
./junk.txt                                               ./third.txt

Grep Command
grep command is the most useful search command. You can use it to find processes
running on system, to find a pattern in a file, etc. It can be used to search one or more
files to match an expression.
It can also be used in conjunction with other commands as in this following example,
output of ps command is passed to grep command, here it means search all processes in
system and find the pattern sleep.
ps -ef | grep sleep will display all the sleep processes running in the system as follows.

       ops   12964   25853   0   16:12:24   ttyAE/AAES   0:00     sleep 60
       dxi   12974   15640   0   16:12:25   ttyAH/AAHP   0:00     sleep 60
       ops   12941   25688   0   16:12:21   ttyAE/AAEt   0:00     sleep 60
       ops   12847   25812   0   16:11:59   ttyAH/AAH6   0:00     sleep 60
       ops   12894   25834   0   16:12:12   ttyAE/AAEX   0:00     sleep 60
       dxi   13067   27253   2   16:12:48   ttyAE/ABEY   0:00     sleep 1
       ops   13046   25761   0   16:12:44   ttyAE/AAE0   0:00     sleep 60
       dxi   12956   13078   0   16:12:23   ttyAG/AAG+   0:00     sleep 60
       ops   12965   25737   0   16:12:24   ttyAE/AAEp   0:00     sleep 60
       ops   12989   25778   0   16:12:28   ttyAH/AAHv   0:00     sleep 60
       ssb   13069   26758   2   16:12:49   ttyAH/AAHs   0:00     grep sleep
       pjk   27049    3353   0   15:20:23   ?            0:00     sleep 3600

       -b option will precede each line with its block number.
       -c option will only print the count of matched lines.
       -i ignores uppercase and lowercase distinctions.
       -l lists filenames but not matched lines.

other associated commands with grep are egrep and fgrep. egrep typically runs faster.
for more information type man egrep or man fgrep in your system.

Find command.
Find command is a extremely useful command. you can search for any file anywhere
using this command provided that file and directory you are searching has read write
attributes set to you ,your, group or all. Find descends directory tree beginning at each
pathname and finds the files that meet the specified conditions. Here are some examples.

Some Examples:
find $HOME -print will lists all files in your home directory.
find /work -name chapter1 -print will list all files named chapter1 in /work directory.
find / -type d -name 'man*' -print will list all manpage directories.
find / -size 0 -ok rm {} \; will remove all empty files on system.

conditions of find

        -atime +n |-n| n will find files that were last accessed more than n or less than -n
         days or n days.
        -ctime +n or -n will find that were changed +n -n or n days ago.
        -depth descend the directory structure, working on actual files first and then
         directories. You can use it with cpio command.
        -exec commad {} \; run the Unix command on each file matched by find. Very
         useful condition.
        -print print or list to standard output (screen).
        -name pattern find the pattern.
        -perm nnnfind files whole permission flags match octal number nnn.
        -size n find files that contain n blocks.
        -type c Find file whole type is c. C could be b or block, c Character special file, d
         directory, p fifo or named pipe, l symbolic link, or f plain file.

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                                    Text processing
cut,paste, sort, uniq,awk,sed,vi.

Cut command.
cut command selects a list of columns or fields from one or more files.
Option -c is for columns and -f for fields. It is entered as
cut options [files]
for example if a file named testfile contains

this is firstline
this is secondline
this is thirdline
cut -c1,4 testfile will print this to standard output (screen)
It is printing columns 1 and 4 of this file which contains t and s (part of this).

       -c list cut the column positions identified in list.
       -f list will cut the fields identified in list.
       -s could be used with -f to suppress lines without delimiters.

Paste Command.
paste command merge the lines of one or more files into vertical columns separated by a
for example if a file named testfile contains

this is firstline
and a file named testfile2 contains
this is testfile2
then running this command
paste testfile testfile2 > outputfile
will put this into outputfile
this is firstline                this is testfile2
it contains contents of both files in columns.
who | paste - - will list users in two columns.

       -d'char' separate columns with char instead of a tab.
       -s merge subsequent lines from one file.

Sort command.
sort command sort the lines of a file or files, in alphabetical order. for example if you
have a file named testfile with these contents

Then running
sort testfile
will give us output of

      -b ignores leading spaces and tabs.
      -c checks whether files are already sorted.
      -d ignores punctuation.
      -i ignores non-printing characters.
      -n sorts in arithmetic order.
      -ofile put output in a file.
      +m[-m] skips n fields before sorting, and sort upto field position m.
      -r reverse the order of sort.
      -u identical lines in input file apear only one time in output.

Uniq command.
uniq command removes duplicate adjacent lines from sorted file while sending one copy
of each second file.

sort names | uniq -d will show which lines appear more than once in names file.


      -c print each line once, counting instances of each.
      -d print duplicate lines once, but no unique lines.
      -u print only unique lines.

Awk and Nawk command.
awk is more like a scripting language builtin on all unix systems. Although mostly used
for text processing, etc.
Here are some examples which are connected with other commands.
df -t | awk 'BEGIN {tot=0} $2 == "total" {tot=tot+$1} END {print
(tot*512)/1000000}' Will give total space in your system in megabytes.
Here the output of command df -t is being passed into awk which is counting the field 1
after pattern "total" appears. Same way if you change $1 to $4 it will accumulate and
display the addition of field 4
which is used space.
for more information about awk and nawk command in your system enter man awk or
man nawk.
Sed command.
sed command launches a stream line editor which you can use at command line.
you can enter your sed commands in a file and then using -f option edit your text file. It
works as
sed [options] files


      -e 'instruction' Apply the editing instruction to the files.
      -f script Apply the set of instructions from the editing script.
      -n suppress default output.

for more information about sed, enter man sed at command line in your system.

Vi editor.
vi command launches a vi sual editor. To edit a file type
vi filename
vi editor is a default editor of all Unix systems. It has several modes. In order to write
characters you will need to hit i to be in insert mode and then start typing. Make sure that
your terminal has correct settings, vt100 emulation works good if you are logged in using
Once you are done typing then to be in command mode where you can write/search/ you
need to hit :w filename to write
and in case you are done writing and want to exit
:w! will write and exit.


      i for insert mode.
           o I inserts text at the curson
           o A appends text at the end of the line.
           o a appends text after cursor.
           o O open a new line of text above the curson.
           o o open a new line of text below the curson.
      : for command mode.
           o <escape> to invoke command mode from insert mode.
           o :!sh to run unix commands.
           o x to delete a single character.
           o dd to delete an entire line
           o ndd to delete n number of lines.
           o d$ to delete from cursor to end of line.
           o    yy to copy a line to buffer.
           o    P to paste text from buffer.
           o    nyy copy n number of lines to buffer.
           o    :%s/stringA/stringb /g to replace stringA with stringB in whole file.
           o    G to go to last line in file.
           o    1G to go to the first line in file.
           o    w to move forward to next word.
           o    b to move backwards to next word.
           o    $ to move to the end of line.
           o    J join a line with the one below it.
      /string to search string in file.
      n to search for next occurence of string.

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                          Shell and programming
Shell programming,bourne shell, ksh, csh, echo,line,sleep, test,cc compiler.

Shell programming concepts and commands.
Shell programming is integral part of Unix operating systems. Shell is command line
userinterface to Unix operating system, User have an option of picking an interface on
Unix such as ksh, csh, or default sh., these are called shells(interface). Shell programming
is used to automate many tasks. Shell programming is not a programming language in the
truest sense of word since it is not compiled but rather an interpreted language. Unix was
written in C language and thus c language is integral part of unix and available on all
versions. Shells, like ksh and csh are popular shells on unix although there are 5 or 6
different shells available but I will only be discussing ksh and csh as well as sh. Common
features among all shells are job control, for example if I am running a processes which is
searching the whole system for .Z files and output is directed to a file named


      find / -name *.Z -print > compressedfiles
       then after entering this command hitting
      <control z>
       key will suspend this job, then entering
      bg
       at command line will put this job in background, entering
      fg
       will put this job in foreground. Entering
      jobs
       at command line will show me all my concurrent jobs that are running.

               Other common features

           o   > will redirect output from standard out (screen) to file or printer or
               whatever you like.
           o   >> filename will append at the end of a file called filename.
           o   < will redirect input to a process or commnand.
           o   | pipe output, or redirect output, good for joining commands, i.e. find
               command with cpio, etc.
           o   & at the end of command will run command in background.
           o   ; will separate commands on same line.
           o   * will match any characters in a file or directories. junk* will match all
               files with first 4 letters
           o   ? will match single characters in a file.
           o   [] will match any characters enclosed.
           o   () execute in subshell.
           o   ` ` to run a command inside another command and use its output.
           o   " " partial quote for variables.
           o   ' ' full quote for variables.
           o   # begin comment (if #/bin/ksh or csh or sh is entered at first line of script
               it runs script in that shell)
           o   bg background execution.
           o   break break from loop statements.
           o   continue Resume a program loop.
           o   Kill pid number will terminate running jobs
           o   stop will stop background job.
           o   suspend will suspend foreground job.
           o   wait will wait for a background job to finish.

Bourne Shell (sh shell).
sh or Bourne shell is default shell of Unix operating systems and is the most simplest
shell in Unix systems.


      cd; ls execute one after another.
      (date;who;pwd)> logifile will redirect all the output from three commands to a
       filenamed logfile.
      sort file | lp will first sort a file and then print it.
      alias [options] [name[='command']] will let you create your own commands.
            o alias ll="ls -la" will execute `ls -la` command whenever ll is entered.
      let expressions is syntax of let statement.
            o let i=i+1 will work as a counter with i incrementing each time this
               statement is encountered.
      for x[in list] do commands done is syntax for for do loop.
      function name {commands;} is the syntax of a function which can be called from
       anywhere in program.
      if condition1 then commands1 elif condition2 then commands2 ... ... ... else
       commands3 fi

Ksh shell (Korn).
Ksh or Korn shell is widely used shell.

Csh or C shell
csh is second most used shell.

Echo command
echo command in shell programming.

Line command.
line command in shell programming.

Sleep command.
sleep command in shell programming.

Test Command.
test command in shell programming.
CC compiler (c programming language compiler).
Since Unix is itself written in C programming language, most Unix operating systems
come with c compiler called cc.

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cu,ftp,login, rlogin,talk,telnet, vacation and write .

Cu command.
cu command is used for communications over a modem or direct line with another Unix
Syntax is
cu options destination


       -bn process lines using n-bit characters (7 or 8).
       -cname Search UUCP's device file and select local area network that matches
       -d Prints diagnostics.
       -e sends even parity data to remote system
       -lline communicate on this device (line=/dev/tty001, etc)
       -n prompts for a telephone number.
       -sn set transmission rate to n(e.g 1200,2400,9600, BPS)


       telno is the telephone number of the modem to connect to.
       system is call the system known to uucp.
       aadr is an address specific to LAN.

Ftp command (protocol).
ftp command is used to execute ftp protocol using which files are transferred over two
Syntax is
ftp options hostname


      -d enable debugging.
      -g disable filename globbing.
      -i turn off interactive prompts.
      -v verbose on. show all responses from remote server.

ftp hostname by default will connect you to the system, you must have a login id to be
able to transfer the files. Two types of files can be transferred, ASCII or Binary. bin at
ftp> prompt will set the transfer to binary. Practice FTP by ftping to nic.funet.fi loggin in
as anomymous with password being your e-mail address.

Login command.
login command invokes a login session to a Unix system, which then authenticates the
login to a system. System prompts you to enter userid and password.

Rlogin command.
rlogin command is used to log on to remote Unix systems, user must have permissions on
both systems as well as same userid, or an id defined in .rhosts file. Syntax is
rlogin options host


      -8 will allow 8 bit data to pass, instead of 7-bit data.
      -e c will let you use escape character c.
      -l user will let you to login as user to remote host, instead of same as local host.

Talk command.
talk command is used to invoke talk program available on all unix system which lets two
users exchange information back and forth in real time. Syntax is
talk userid@hostname

Telnet command.
Telnet command invokes a telnet protocol which lets you log on to different unix, vms or
any machine connected over TCP/IP protocol, IPx protocol or otherwise. Syntax is
telnet hostname

Vacation command.
vacation command is used when you are out of office. It returns a mail message to sender
announcing that you are on vacation. to disable this feature, type mail -F " " .
syntax is
vacation options


      -d will append the date to the logfile.
      -F user will forward mail to user when unable to send mail to mailfile.
      -l logfile will record in the logfile the names of senders who received automatic
      -m mailfile will save received messages in mailfile.

Write command will initiate an interactive conversation with user. Syntax is
write user tty

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                              Storage commands
compress uncompress, cpio,dump,pack, tar, mt.

Compress command.
Compress command compresses a file and returns the original file with .z extension, to
uncompress this filename.Z file use uncompress filename command. syntax for compress
command is
compress options files


      -bn limit the number of bits in coding to n.
      -c write to standard output (do not change files).
      -f compress conditionally, do not prompt before overwriting files.
      -v Print the resulting percentage of reduction for files.

Uncompress command.
Uncompress file uncompresses a file and return it to its original form.
syntax is
uncompress filename.Z this uncompresses the compressed file to its original name.


      -c write to standard output without changing files

Cpio command.
cpio command is useful to backup the file systems. It copy file archives in from or out to
tape or disk, or to another location on the local machine. Its syntax is
cpio flags [options]

       It has three flags, -i, -o, -p

      cpio -i [options] [patterns]
           o cpio -i copy in files who names match selected patterns.
           o If no pattern is used all files are copied in.
           o It is used to write to a tape.

               cpio -o

           o   Copy out a list of files whose name are given on standard output.

               cpio -p

           o   copy files to another directory on the same system.


           o   -a reset access times of input files.
           o   -A append files to an archive (must use with -o).
           o   -b swap bytes and half-words. Words are 4 bytes.
           o   -B block input or output using 5120 bytes per record.
           o   -c Read or write header information as Ascii character.
           o   -d create directories as needed.
           o   -l link files instead of copying.
           o   -o file direct output to a file.
           o   -r rename files interactively.
           o   -R ID reassign file ownership and group information to the user's login ID.
           o   -V print a dot for each file read or written.
           o   -s swap bytes.
           o   -S swap half bytes.
           o   -v print a list of filenames.


           o   find . -name "*.old" -print | cpio -ocvB > /dev/rst8 will backup all *.old
               files to a tape in /dev/rst8
           o   cpio -icdv "save"" < /dev/rst8 will restore all files whose name contain
           o   find . -depth -print | cpio -padm /mydir will move a directory tree.

Dump command is useful to backup the file systems.
dump command copies all the files in filesystem that have been changed after a certain
date. It is good for incremental backups. This information about date is derived from
/var/adm/dumpdates and /etc/fstab .
syntax for HP-UX dump is
/usr/sbin/dump [option [argument ...] filesystem]


      0-9 This number is dump level. 0 option causes entire filesystem to be dumped.
      b blocking factor taken into argument.
      d density of tape default value is 1600.
      f place the dump on next argument file instead of tape.
      This example causes the entire file system (/mnt) to be dumped on
       /dev/rmt/c0t0d0BEST and specifies that the density of the tape is 6250 BPI.
           o /usr/sbin/dump 0df 6250 /dev/rmt/c0t0d0BEST /mnt
      for more info type man dump at command line.

Pack command.
pack command compacts each file and combine them together into a filename.z file. The
original file is replaced. Pcat and unpack will restore packed files to their original form.
Syntax is
Pack options files

       - Print number of times each byte is used, relative frequency and byte code.
       -f Force the pack even when disk space isn't saved.

       To display Packed files in a file use pcat command
        pcat filename.z
       To unpack a packed file use unpack command as unpack filename.z .

Tar command.
tar command creates an archive of files into a single file.
Tar copies and restore files to a tape or any storage media. Synopsis of tar is
tar [options] [file]

tar cvf /dev/rmt/0 /bin /usr/bin creates an archive of /bin and /usr/bin, and store on the
tape in /dev/rmt0.
tar tvf /dev/rmt0 will list the tape's content in a /dev/rmt0 drive.
tar cvf - 'find . -print' > backup.tar will creates an archive of current directory and store it
in file backup.tar.


       c creates a new tape.
       r append files to a tape.
       t print the names of files if they are stored on the tape.
       x extract files from tape.


       b n use blocking factor of n.
       l print error messages about links not found.
       L follow symbolic links.
       v print function letter (x for extraction or a for archive) and name of files.

Mt command
Mt command is used for tape and other device functions like rewinding, ejecting, etc. It
give commands to tape device rather than tape itself. Mt command is BSD command and
is seldom found in system V unix versions.
syntax is
mt [-t tapename] command [count]
       mt for HP-UX accept following commands

      eof write count EOF marks.
      fsf Forward space count files.
      fsr Forward space count records.
      bsf Backward space count files.
      bsr Backward space count records.
      rew Rewind tape.
      offl Rewind tape and go offline.
      eod Seek to end of data (DDS and QIC drives only).
      smk Write count setmarks (DDS drives only).
      fss Forward space count setmarks (DDS drives only).
      bss Backward space count setmarks (DDS drives only).
      Examples
           o mt -t /dev/rmt/0mnb rew will rewind the tape in this device.
           o mt -t /dev/rmt/0mnb offl will eject the tape in this device.

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                                   System Status
at, chmod,chgrp, chown,crontab,date, df,du, env, finger, ps,ruptime, shutdwon,stty, who.

At command.
at command along with crontab command is used to schedule jobs.
at options time [ddate] [+increment] is syntax of at command.
for example if I have a script named usersloggedin which contains.

who | wc -l
echo "are total number of people logged in at this time."
and I want to run this script at 8:00 AM. So I will first type at 8:00 %lt;enter>
usersloggedin %lt;enter>
I will get following output at 8:00 AM
are total number of people logged in at this time.

      -f file will execute commands in a file.
      -m will send mail to user after job is completed.
      -l will report all jobs that are scheduled and their jobnumbers.
       -r jobnumber will remove specified jobs that were previously scheduled.

Chmod command.
chmod command is used to change permissions on a file.
for example if I have a text file with calender in it called cal.txt.
initially when this file will be created the permissions for this file depends upon umask
set in your profile files. As you can see this file has 666 or -rw-rw-rw attributes.

ls -la cal.txt

-rw-rw-rw-         1 ssb        dxidev          135 Dec     3 16:14 cal.txt

In this line above I have -rw-rw-rw- meaning respectively that owner can read and
write file, member of the owner's group can read and write this file and anyone else
connected to this system can read and write this file., next ssb is owner of this file
dxidev is the group of this file, there are 135 bytes in this file, this file was created on
December 3 at time16:14 and at the end there is name of this file. Learn to read these
permissions in binary, like this for example Decimal 644 which is 110 100 100 in binary
meand rw-r--r-- or user can read,write this file, group can read only, everyone else can
read only. Similarly, if permissions are 755 or 111 101 101 that means rwxr-xr-x or user
can read, write and execute, group can read and execute, everyone else can read and
execute. All directories have d in front of permissions. So if you don't want anyone to see
your files or to do anything with it use chmod command and make permissions so that
only you can read and write to that file, i.e.
chmod 600 filename.

Chgrp command.
chgrp command is used to change the group of a file or directory.
You must own the file or be a superuser.
chgrp [options] newgroup files is syntax of chgrp.
Newgroup is either a group Id or a group name located in /etc/group .


       -h will change the group on symbolic links.
       -R recursively descend through directory changing group of all files and
Chown command.
chown command to change ownership of a file or directory to one or more users.
Syntax is
chown options newowner files


        -h will change the owner on symbolic links.
        -R will recursively descend through the directory, including subdirectories and
         symbolic links.

Crontab command.
crontab command is used to schedule jobs. You must have permission to run this
command by unix Administrator. Jobs are scheduled in five numbers, as follows.

 Minutes                      0-59
                                       Hour                         0-23
                                       Day of month         1-31
                                       month                        1-12
                                       Day of week                  0-6 (0 is sunday)
so for example you want to schedule a job which runs from script named backup_jobs in
/usr/local/bin directory on sunday (day 0) at 11.25 (22:25) on 15th of month. The entry in
crontab file will be. * represents all values.
 25 22     15 * 0 /usr/local/bin/backup_jobs
The * here tells system to run this each month.
Syntax is
crontab file So a create a file with the scheduled jobs as above and then type
crontab filename .This will scheduled the jobs.

Date command.
Date displays todays date, to use it type date at prompt.

Sun Dec     7 14:23:08 EST 1997
is similar to what you should see on screen.

Df command.
df command displays information about mounted filesystems. It reports the number of
free disk blocks. Typically a Disk block is 512 bytes (or 1/2 Kilobyte).
syntax is
df options name

      -b will print only the number of free blocks.
      -e will print only the number of free files.
      -f will report free blocks but not free inodes.
      -F type will report on an umounted file system specified by type.
      -k will print allocation in kilobytes.
      -l will report only on local file systems.
      -n will print only the file system name type, with no arguments it lists type of all

Du command.
du command displays disk usage.

Env command.
env command displays all the variables.

Finger command.
finger command.

PS command
ps command is probably the most useful command for systems administrators. It reports
information on active processes.
ps options


      -a Lists all processes in system except processes not attached to terminals.
      -e Lists all processes in system.
      -f Lists a full listing.
      -j print process group ID and session ID.

Ruptime command.
ruptime command tells the status of local networked machines.
ruptime options

      -a include user even if they've been idle for more than one hour.
      -l sort by load average.
      -r reverse the sort order.
      -t sort by uptime.
      -i sort by number of users.

Shutdown command.
Shutdown command can only be executed by root. To gracefully bring down a system,
shutdown command is used.


      -gn use a grace-period of n seconds (default is 60).
      -ik tell the init command to place system in a state k.
            o s single-user state (default)
            o 0 shutdown for power-off.
            o 1 like s, but mount multi-user file systems.
            o 5 stop system, go to firmware mode.
            o 6 stop system then reboot.
      -y suppress the default prompt for confirmation.

Stty command
stty command sets terminal input output options for the current terminal. without options
stty reports terminal settings.
stty options modes < device


      -a report all options.
      -g report current settings.


      0 hang up phone.
      n set terminal baud.
      erase keyname, will change your keyname to be backspace key.
Who command
who command displays information about the current status of system.
who options file
Who as default prints login names of users currently logged in.


      -a use all options.
      -b Report information about last reboot.
      -d report expired processes.
      -H print headings.
      -p report previously spawned processes.
      -u report terminal usage.

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                   Advance unix command concepts
Put advance commands utilities, redirection, etc here.

cal > cal.txt To create a new file called cal.txt that has calendar for current month. > sign
redirects output from stdout (screen) to a file.

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Top of page

Fundamentals of                                                          Shell
                        Unix commands         User Accounts
Unix                                                                     Programming
File Systems            Networking            Backups                    Security
                        Installing            Performance and            Some Useful
Installing software
                        Hardware              Tuning                     Scripts

                           Copyrighted by Sandeep singh Bajwa.

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