Linux Command 1

8/6/2019 Linux Command 1

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Command Summary Use

Use cd to change

directories

Type cd followed by the name of a directory to access that

directory.

Keep in mind that you are always in a directory and allowed access

to any directories hierarchically above or below. You may also

benefit from reviewing my directory commands page.Ex:cd games

If the directory games is not located hierarchically below the

current directory, then the complete path must be written out. Ex:cd /usr/games

To move up one directory, use the shortcut command. Ex:cd ..

Use clear to clear thecommand prompt

Type clear to clean up your command prompt window.

This is especially helpful when you are typing lots of commandsand need a clean window to help you focus.Ex:

clearThis is also useful when you are getting ready to type a rather long

command and do not wish to become confused by other details on

the screen. Brought to you by Reallylinux.com

Use date to set yourserver's date and time

Type date followed by the two digit month, the two digit date, the

two digit time, and two digit minutes. The syntax is easy enoughand resembles this: MMDDhhmm

This command is helpful but must be used when superuser or

logged in as root.

You can get more help with administrator commands by clickingthis link . Note that if you don't use root, you will get an "Operation

not permitted" reply.As root user you can use thecommand such as:date 11081300

The above command will set the server date and time to the 11th

month (November), the 8th day, at 1:00pm.

Use df to check disk space

Typing df provides a very quick check of your file system disk

space.

Type df -h to get a more easily readable version of the output.Notice that this command will include all applicable storage such

as your hard disk/s (hda, hdb etc.) and your server SWAP file(shm). To list disk space including filesystem type:df -h -T

Use finger to see who's

on the system

Typing finger allows you to see who else is on the system or get

detailed information about a person who has access to the system.

Type finger followed by the name of a user's account to getinformation about that user. Or, type finger and press enter to see



who's on the system and what they are doing. Ex:finger johndoe

Use logout to quit usingthe system

Yep, you guessed it, typing logout will log your account out of the

system.

Type logout at the prompt to disconnect from your Linux machineor to logout a particular user session from the system. Keep in mind

that although rudimentary, leaving your critical account logged on

may be a security concern. We always recommend promptly usinglogout when you are finished using your root account! Ex:logout

Use ls to list files and

directories

Type ls to see a list of the files and directories located in the

current directory. If you’re in the directory named games and youtype ls, a list will appear that contains files in the games directory

and sub-directories in the games directory. Examples:ls Maills /usr/bin

Type ls -alt to see a list of all files (including .rc files) and alldirectories located in the current directory. The listing will include

detailed, often useful information. Examples:ls -altls -alt /usr/bin

If the screen flies by and you miss seeing a number of files, tryusing the |more at the end like:ls -alt |more

* In Bash (Linux shell) often the abbreviated command L is

available. To get a verbose listing of files and directories you couldtherefore simply type: l

Use man to pull upinformation about a Linux

command

Type man followed by a command to get detailed information

about how to use the command. Ex:man ls

Type man -k followed by a word to list all of the commands and

descriptions that contain the word you specified. Ex:man -k finger

Use more to read thecontents of a file

Type more followed by the name of a text file to read the file’s

contents. Why do we exmphasize using this on a "text" file?Because most other types of files will look like garbage! Ex:more testfile.txt

Use nano to start a texteditor

Typing nano will start a basic text editor on most Linux systems.Type nano followed by the filename you wish to edit. This basic

editor is quick and easy to use for beginners. However, it is very

important that you also learn about other text editors available on



Linux and UNIX systems. Click on this link to learn about otherslike emacs, vi, and pico. Ex:nano /etc/security/access.conf

Use passwd to change

your current password

Type passwd and press enter. You'll see the message Changing

password for yourname.At the Old password: prompt, type in your old password .

Then, at the Enter new password: prompt, type in your new

password .The system double checks your new password. Beside the Verify:

prompt, type the new password and press again.

Create a secure password that combines parts of words and

numbers. For instance, your dog's name may be Rufus. He may

have been born in 1980. Create a password that uses parts of boththe name and date of birth, such as 80rufuS. Note the use of at least

one capital letter. This is a fairly secure password and easy toremember.

Use pwd to list the name of

your current directory

Type pwd and hit enter. You'll see the full name of the directory

you are currently in. This is your directory path and is very handy.This is especially handy when you forget which directory you’ve

changed to and are trying to run other commands.

Manipulating Files - Linux Commands

Command Summary Use

chmod The chmod command allows you to alter accessrights to files and directories. All filesand directories have security permissionsthat grant the user particular groups’ or allother users’ access.

To view your files' settings, at the shellprompt type: ls -alt

You should see some files with the followingin front of them (an example follows):

total 4drwxrwsr-x 7 reallyli reallyli 1024 Apr 6 14:30 .drwxr-s--x 22 reallyli reallyli 1024 Mar 30 18:20 ..d-wx-wx-wx 3 reallyli reallyli 1024 Apr 6 14:30contentdrwxr-xr-x 2 reallyli reallyli 1024 Mar 25 20:43 files

What do the letters mean in front of thefiles/directories mean?r indicates that it is readable (someone can



view the file’s contents)w indicates that it is writable (someone canedit the file’s contents)x indicates that it is executable (someonecan run the file, if executable)- indicates that no permission to manipulate

has been assigned

When listing your files, the first characterlets you know whether you’re looking at afile or a directory. It’s not part of thesecurity settings. The next three charactersindicate Your access restrictions. The nextthree indicate your group's permissions, andfinally other users' permissions.

Use chmod followed by the permission you

are changing. In very simple form this would

be:chmod 755 filename The example above will grant you full rights,group rights to execute and read, and allothers access to execute the file.

# Permission

7 full

6 read and write

5 read and execute

4 read only

3 write and execute

2 write only

1 execute only

0 none

Still confused? Use the table above to definethe settings for the three "users." In thecommand, the first number refers to your permissions, the second refers to group, andthe third refers to general users.

Typing the command: chmod 751 filename

gives you full access, the group read andexecute, and all others execute onlypermission.

cp Type cp followed by the name of an existing



file and the name of the new file.

Ex:cp newfile newerfileTo copy a file to a different directory(without changing th

e file’s name), specify the directory insteadof the newfilename. Ex:cp newfile testdirTo copy a file to a different directory andcreate a new file name, you need to specify adirectory/a new file name. Ex:cp newfile testdir/newerfilecp newfile ../newerfileThe .. represents one directory up in thehierarchy.

file Type file followed by the name of an existingfile in the directory.

Ex:file emergency3_demo.exe

OUTPUT: MS-DOS executable (EXE)

This command allows you to figure out whatthe file type is and how to use it. Forinstance the command will tell you whether itis an executable, a compressed file and whichtype, or something unusual.

This command is simplistic, but often canallow you to determine why a file does notrespond the way you expect.

mv Type mv followed by the current name of afile and the new name of the file.

Ex:mv oldfile newfile

Type mv followed by the name of a file andthe new directory where you'd like to placethe file. Ex:mv newfile testdirThis moves the file named newfile to anexisting directory named testdir. Be certainyou’re specifying a directoryname or the mv command alters the name of thefile instead of moving it.



rm Type rm followed by the name of a file toremove the file.

Ex:rm newfileUse the wildcard character to remove several

files at once. Ex:rm n*This command removes all files beginning withn.Type rm -i followed by a filename if you’dlike to be prompted before the file isactually removed. Ex:rm -i newfilerm -i n*By using this option, you have a chance toverify the removal of each file. The -ioption is very handy when removinga number of files using the wildcard

character *.

This list only has items related to files, but this link will take you to the page related tocommands for directories.

Directory Related Commands

Command Summary Use

cd Use cd to change directories. Type cdfollowed by the name of a directory to access

that directory. Keep in mind that you arealways in a directory and can navigate todirectories hierarchically above or below.Ex:cd gamesIf the directory games is not locatedhierarchically below the current directory,then the complete path must bewritten out. Ex:cd /usr/gamesTo move up one directory, use the shortcutcommand. Ex:cd ..

Use cp -r to copy a directory and all of itscontentsType cp -r followed by the name of anexisting directory and the name of the newdirectory. Ex:cp -r testing newdirYou must include the -r or you’ll see thefollowing message:



cp: testing is a directory and -r notspecified.This command saves you time if you need tomake a mirror image of a directory packedwith files.

mkdir Use mkdir to make/create a brand newdirectoryType mkdir followed by the name of adirectory. Ex:mkdir testdir

mv Use mv to change the name of a directoryType mv followed by the current name of adirectory and the new name of the directory.Ex:mv testdir newnamedir

pwd

Trying to find out where on your Linux serveryou currently are located? The pwd (printworking directory) command will show you thefull path to the directory you are currentlyin. This is very handy to use, especiallywhen performing some of the other commands onthis page!

rmdir Use rmdir to remove an existing directory(assuming you have permissions set to allowthis).

Type rmdir followed by a directory's name toremove it. Ex:rmdir testdir

You CAN'T remove a directory that containsfiles with this command.

Instead to delete non-empty directories inLinux, use the more useful command:rm -r

This command removes directories and fileswithin the directories. Read more detailsabout this in Commands for Beginning Admins

The rmdir command is used mostly to removeempty directories. If you have a desire touse this command then you'll need to deleteor move the files before attempting to removea full directory. For more help please readthe mv command and also File RelatedCommands.



Command Summary Use

du

The du command prints a summary of the amountof information you have stored in yourdirectories on the mounted disks.syntax: du [options] pathex: du -a /News

Options:-s print the sum of bytes in your directories-a print a line for each file in yourdirectory

grep

The grep command searches text files for aparticular word or string of words. Very

helpful when trying to find that needle in ahaystack, like a particular line in a largelog file.syntax: grep textstring filename(s)ex: grep century history.text.doc

Head

Tail

head: prints the beginning of a text filetail: prints the end of a text fileThese commands allow you to view parts of atext file.

tail -n 5 textfile.txthead -n 5 textfile.txt The examples above will print the last 5lines of the file textfile.txt and then thefirst 5 lines.

locate

Trying to find out where on your Linux servera particular file resides? Having a realnasty time doing it? If you have the Bashshell you can try using the locate command toidentify where it is on your mounted drives.Type: locate filename and press enter.Replace filename with the name of the fileyou are looking for. This is a real timesaving command as you start navigating yourLinux server!If locate does not work for you try using

which.

Nice

Nohup

Nice: runs programs/commands at a lowersystem priority Nohup: runs nice programs even when you’relogged off the systemBy using the two commands simultaneously,your large processes can continue to run,even when you have logged off the system andare relaxing.



Ex: nice nohup c program.c .This command will allow the c compiler tocompile program.c even when you have loggedoff the system.

ps

related to "stopped jobs"

The ps command displays all of the existingprocesses. This command is also directly

linked to issues with stopped processes (alsoknown as "stopped jobs").Occasionally, you may see the message Thereare Stopped Jobs. If you log off the system without properlystopping your jobs, some jobs/processes mayremain in memory tying up the system anddrawing unnecessary processing bandwidth.

Type ps and hit enter. This will list all ofyour current processes running, or stopped.

PID TT STAT TIME COMMAND

23036 pl S 0:00 -csh23070 pl R 0:00 vi

The number under PID is the processidentification number. To kill a process thatis stopped , type: kill pid . Replace pid withthe exact number of the process.Ex: While in Vi, you accidentally press thewrong keys. Vi's operation is stopped and youare kicked back to the prompt. To kill thestopped Vi command, you may type: kill 23070.

stty

The stty command allows you to view a listingof your current terminal options. By usingthis command, you can also remap keyboardkeys, tailoring to your needs.Ex: stty and hit enter. This lists yourterminal settings.Ex: stty erase\^h . This remaps your erasekey (backspace) to the Ctrl and h keys. Fromnow on, holding down Ctrl and pressing h willcause a backspace. So you're scratching yourhead asking why is this handy? You'll see howhelpful it can be to use.

talk

In order to contact someone who is on thesystem, at the prompt you type: talk

accountname . Replace accountname with thefull account name of the person. If you don’twant anyone to disturb you using the talkcommand, at the prompttype: mesg n. This prevents others from usingtalk to reach you.

tar

also related to gzip

You're bound to come across files that are g-zipped and tarred. Okay, now what? These aremethods of compressing and storing



directories and files in a single "file."Most new Linux programs come off the web assomething like coolnew-game.4-4-01.gz. Thisfile is likely a tar file that has then beengzipped for compression. The way to handlethese files is simple, but requires that you

put the file into an appropriate directory.In other words, don't place the file in yourroot or /bin unless it belongs there.

Now you can do a one fell swoop un-gzip itand untar it into its original form (usuallymultiple files in many sub directories) by

typing: tar -xvzf *.gz

This will programmatically un-gzip and thenuntar all files in the current directory intotheir full original form including sub-directories etc. Please be careful where andhow you run this!

w

This command allows you to list all users’and their processes who are currently loggedin to the Linux server, or a particularuser’s processes. Type: w to view all users’processes. Type: w jsmith to view jsmith’sprocesses. We use this all the time from asystem admin standpoint. Please also see morecommands to get user information on thispage. You need to know who logs on to yoursystem! Okay, so you have a stand alone Linuxbox and no one else uses it? Try this command

just to be sure. ;)

!!

Don’t waste time and energy retyping commandsat the prompt. Instead, use the ! option. Toautomatically re-display the last command youtyped at the prompt, type: !! and pressenter. Press again to invoke the command. Youcan also automatically re-display a commandyou typed earlier by using the ! and thefirst few letters of the command.Ex: At the Linux prompt you had typed thecommand clear , followed by the command pico,followed by the command ftp. In order to re-display the clear command you type: !cl andpress enter. In order to re-display the lastcommand you typed, simply type: !! . Try itout. You’ll find this a time saver whendealing with long commands. Especiallycommands like tar!

Basic Linux Commands



Command Example Description

cat Sends file contents to standard output. This is a way to

list the contents of short files to the screen. It works wellwith piping.

cat .bashrc Sends the contents of the ".bashrc" file to the screen.

cd Change directory

cd /home Change the current working directory to /home. The '/'

indicates relative to root, and no matter what directoryyou are in when you execute this command, the directory

will be changed to "/home".

cd httpd Change the current working directory to httpd, relative tothe current location which is "/home". The full path of

the new working directory is "/home/httpd".

cd .. Move to the parent directory of the current directory.

This command will make the current working directory

"/home.

cd ~ Move to the user's home directory which is

"/home/username". The '~' indicates the users home

directory.

cp Copy files

cp myfile yourfile Copy the files "myfile" to the file "yourfile" in the

current working directory. This command will create the

file "yourfile" if it doesn't exist. It will normallyoverwrite it without warning if it exists.

cp -i myfile yourfile With the "-i" option, if the file "yourfile" exists, you will

be prompted before it is overwritten.cp -i /data/myfile . Copy the file "/data/myfile" to the current working

directory and name it "myfile". Prompt before

overwriting the file.

cp -dpr srcdir destdir Copy all files from the directory "srcdir" to the directory"destdir" preserving links (-p option), file attributes (-p

option), and copy recursively (-r option). With these

options, a directory and all it contents can be copied to

another directory.

dd dd if=/dev/hdb1

of=/backup/

Disk duplicate. The man page says this command is to

"Convert and copy a file", but although used by more

advanced users, it can be a very handy command. The"if" means input file, "of" means output file.

df Show the amount of disk space used on each mounted

filesystem.

less less textfile

Similar to the more command, but the user can page upand down through the file. The example displays the

contents of textfile.



ln Creates a symbolic link to a file.

ln -s test symlink Creates a symbolic link named symlink that points to thefile test Typing "ls -i test symlink" will show the two

files are different with different inodes. Typing "ls -l test

symlink" will show that symlink points to the file test.

locate A fast database driven file locator.

slocate -u This command builds the slocate database. It will take

several minutes to complete this command. This

command must be used before searching for files,

however cron runs this command periodically on mostsystems.

locate whereis Lists all files whose names contain the string "whereis".

logout Logs the current user off the system.

ls List files

ls List files in the current working directory except those

starting with . and only show the file name.

ls -al List all files in the current working directory in long

listing format showing permissions, ownership, size, andtime and date stamp

more Allows file contents or piped output to be sent to the

screen one page at a time.

more /etc/profile Lists the contents of the "/etc/profile" file to the screenone page at a time.

ls -al |more Performs a directory listing of all files and pipes the

output of the listing through more. If the directory listing

is longer than a page, it will be listed one page at a time.

mv Move or rename files

mv -i myfile yourfile Move the file from "myfile" to "yourfile". This

effectively changes the name of "myfile" to "yourfile".

mv -i /data/myfile . Move the file from "myfile" from the directory "/data" tothe current working directory.

pwd Show the name of the current working directory

more /etc/profile Lists the contents of the "/etc/profile" file to the screen

one page at a time.

shutdown Shuts the system down.

shutdown -h now Shuts the system down to halt immediately.

shutdown -r now Shuts the system down immediately and the system

reboots.

whereis Show where the binary, source and manual page files arefor a command

whereis ls Locates binaries and manual pages for the ls command.



Editors: emacs, vi, pico, jed, vim

Viewing, copying, moving and deleting files

ls Display the contents of the current directory

ls -a Display also hidden files and hidden directories

cp filename /path/dir_name Copy filename into directory /path/dir_name

cp -r dir_name /path/dir_name2 Copy the entire dir_name into /path/dir_name2

cp filename1 filename2

/path/dir_nameCopy filename1 and filename2 into /path/dir_name

rm name Remove a file or directory called name

rm -r nameRemove an entire directory as well as its included files and

subdirectories

mv filename /path/dir_name Move filename into /path/dir_name

mv filename1 filename2 Rename filename1 to filename2

cat filename Display filenames contents

more filename Display filename in pages. Use spacebar to view next page

head filename Display filenames first 10 lines

head -15 filename Display filenames first 15 lines

tail filename Display filenames last 10 lines



tail -15 filename Display filenames last 15 lines

pwd Display current directory

cd /path/dir_name Change to directory /path/dir_name

cd .. Go 1 directory up

mkdir dir_name Create directory dir_name

rmdir dir_name Delete directory dir_name

Finding files and text within files

updatedbUpdate (create first time used) a database of all files under the root directory

/

locate filename Find file filename searching in the database

find / -name filename Starting from the root directory search for the file called filename

find / -name *filename Same as above but search for file containing the string filename

grep string

/path/dir_nameStarting from /path/dir_name search for all files containing string

which application_name Search $path for application app_name

whereis application_name Search $path, man pages and source files for application_name

Archived files



Decompress

tar -xzf filename.tgz Decompress tzg file

tar -xzf filename.tar.gz Decompress tar.gz file

tar -xjf filename.tar.bz2 Decompress tar.bz2 file

Compress

tar -czf filename.tar /path/dir_name Compress directory /path/dir_name to filename.tar

gzip -c filename > filename.gz Compress /path/dir_name to filename.tar.gz

bzip2 -c filename > filename.bz2 Compress /path/dir_name to filename.tar.bz2

Using rpm files

rpm -hiv package.rpm Install rpm called package.rpm

rpm -hiv --force package.rpm Install rpm called package.rpm by force

rpm -hUv package.rpm Upgrade rpm called package.rpm

rpm -e package.rpm Delete rpm called package.rpm

rpm -qpil package.rpm List files in not-installed rpm called package.rpm

rpm -ql package.rpm List files in installed rpm called package.rpm

rpm -q str List installed rpms containing the string str

rpm -qf /path/application_name Display the rpm that contains application application_name

Starting and Stoping

startx Start the X system

shutdown -h now Shutdown the system now and do not reboot



halt Same as above

shutdown -r now Reboot

reboot Same as above

shutdown -r +10 Reboot in 10 minutes

Mounting filesystems

mount -t vfat /dev/sd(a)(1)

/mnt/c_drive

Mount the first partition 1 of the first hard disk drive a which is in fat32

vfat dormat under /mnt/c_drive directory

mount -t iso9660 /dev/cdrom

/mnt/cdromMount cdrom under /mnt/cdrom directory

umount /mnt/hda1 Unmout the above

User administration

users Display users currently logged in

adduser username Create a new user called username

passwd username Define password for user called username

who List logged-in users

whoami Display current user

finger username Displays info about user username

su Log in as root from current login

su - Log in as root from current login and take root's path

exit Exit from console login (ie, logout).

Processes



command Execute command in the foreground

command & Execute command in the background

ctrl+z Suspend a program

ctrl+c Interrupt a program

ps List all processes

kill -9 pid Kill process with id pid

top Monitor processes in real time

Networking

hostname List the system's hostname

ifconfig Set/Display network information

host ip Resolves ip's hostname

ping ip/hostname Check if ip/hostname is reachable

traceroute ip/hostname Find network path to ip/hostname

System Information

uname -a General system information

fdisk -l List partition tables

cp filename /path/dir_name Copy filename into directory /path/dir_name

df -T -h List filesystem disk space usage

lspci List PCI devices

lsusb List USB devices

free -m Display RAM+Swap usage



Program Compile

gcc -o output file.c Compile a C program

./output Run a C program you have compiled

g++ -o output file.cpp Compile a C++ program

./output Run a C++ program you have compiled

./configure && make && su -c 'make install' Configure, compile and install a program with Makefile

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