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Table of Contents
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a2enmod
Enable/disable or view modules for apache server.
acpi
Shows battery and thermal information. Try with -t for thermal.
adduser/addgroup
Add a user or group to the system
For example "adduser reza" adds user reza to the system, "addgroup admin" adds group admin to the system, "adduser reza admin" adds user reza to admin group.
Add users to the end of /etc/sudoers to give them sudo privileges. That file is so flexible for example you can add root capability to a group, etc.
See usermod.
In CentOS sudo is not installed by default and you should install it first using yum install sudo.
alias
For example alias lh="ls -l -a $HOME" makes the command "lh" become equivalent to the longer command "lh -l -a $HOME". You can use it in bash profile and assign a simple alias to a long and frequently used command.
apt
| apt-cache search clone | Searches the packages indexes for the clone name |
| apt-cache show sun-java6-bin | see info about that package |
| apt-get autoremove | removes packages that were automatically installed to satisfy dependencies for some package and that are no more needed |
| apt-get purge x | remove x with all its configuration files, etc. |
| apt-get remove the-package | removes the-package |
| apt-get update | Updates the package indexes |
| apt-get upgrade | Installs the newest packages |
Background Command
put & at the end of any command and it will be take to the background meaning that the command line will be freed so that you can keep typing. This is very useful and you do not need to open another command line.
bg
Shows the last stopped command using Ctrl-Z. See fg.
cal
Display a calendar
cat
Display the contents of a file
cat file_name | grep —color some_text
chkconfig
Updates and queries runlevel information for system services.
Adding to it: chkconfig —add the_script. Notice that the_script should be chkconfig friendly. See a section in linux-how-to
chgrp
| Command | Desc |
| chgrp user file | Makes file belong to the group user |
chmod
chmod [references][operator][modes] file1 …
Reference: u (user), g (group), o (others), a (all)
Operator: +, -, =
Mode: r, w, x, X, s, t
| Command | Desc |
| chmod ug+rw sample | Adds the read and write permissions to the user and group for that file |
| chmod +x ss | Anyone can execute the file ss |
| chmod og=r archive.sh | others and group have read access |
chown
| Command | Desc |
| chown cliff file | Makes cliff the owner of file |
| chown -R cliff dir | Makes cliff the owner of dir and everything in its directory tree |
cp
Copy files and directories. To copy a dir with content use "cp -r source dest" or "cp -r * dest" copies everything in current directory to dest.
crontab
"crontab -l" show all the cron jobs for the current user.
CTRL-R
To search in the history of your commands use the CTRL-R key to perform a “reverse-i-search”.
Press CTRL-R then start typing. After you have typed what you are looking for, use the CTRL-R key combination to go through the history.
Use [Enter] to execute it. Alternatively, using the right or left arrow keys will place the command on an actual command-line so you can edit it.
date
Shows date and time
df
Display disk space information
dos2unix
Convert DOS/Windows format to ISO/Unix/Linux format. dos2unix original_file dest_file. It is good to fix specially eol/eof.
dpkg
Package manager for debian. To install a package do: sudo dpkg -i x.deb
du
Gives the disk usage.
du -sh /dir gives the directory size. h stands for human readable and s is for summary.
env
Environment variables
export
- export shows some env stuff
- export CASROOT=/usr/local/CAS3.0 Defines the environment variable CASROOT
- export PATH=$PATH:$HOME/bin I am setting the PATH environment variable to the previous value of itself, followed by a colon, and a directory-name formed from the HOME variable and "/bin"
echo
echo $CASROOT Prints out the value of CASROOT, or /usr/local/CAS3.0
egrep
Similar to grep but understands full regular expressions: cat file | egrep "NAME|VERSION"
fg
Goes to the last stopped command using Ctrl-Z. See bg.
find
Searches for files by name, etc.
| Command | Desc |
| find search_path -name filename | Normal usage |
| find . -name aaa.txt | Finds all the files named 'aaa.txt' in the current directory or any subdirectory tree |
| find . -name *.sql | accepts wildcards |
| find / -name vimrc | Find all the files named 'vimrc' anywhere on the system |
| find /usr/local/games -name "*xpilot*" | Find all files whose names contain the string 'xpilot' which exist within the '/usr/local/games' directory tree |
| find / -name 'mypage.htm' | search for any file named mypage.htm on the root and all subdirectories from the root |
| find /backups/ -type f -mtime +5 -exec rm {} \; | Finds are the files in that directory older than 5 days and deletes them! |
If you get "Permission denied", do it with sudo.
You can combine find and grep. As an example: find . -name build.xml | grep java
free
Displays the amount of free and used memory in the system. Use free -m to display in megabytes.
ftp
| Command | Desc |
| ftp | goes into ftp shell |
| open | open www.xxx.com to open the remote host using port 22 |
| cd | change directory after login |
| get | get a file and copy into your local folder |
| put | upload a file into the host |
| binary or ascii | To transfer a file in binary or ascii mode. Some ftp clients go back to ascii mode when you enter an ls or dir command. To be safe, always use the binary command before getting a binary file. |
gksudo
Is a front end for sudo which sucks.
grep
Is a very powerful search tool! Can search the content of files or output of another command.
| Options | Desc | Example |
|---|---|---|
| grep test *.* | search for the test in all file in the same directory | similar to grep test . or grep "test" . |
| -r | Resursive | grep -r "reza" . OR in SunOS grep searchText *.* |
| -d recurse | same as -r | |
| -n | line number | |
| -i | case in-sensitive | |
| —color | add color |
groupmod
modify groups.
groups
Returns the user's groups. See whoami and id.
gzip
gzip -dc file | less
history
A list of previously ran commands. You can do !! instead too.
ifconfig
/sbin/ifconfig -a
jobs
Shows stopped commands using Ctrl+Z.
kill
kill <PID> kills a process . if it does not work then use kill -9 <PID>. See pkill
last
shows information about the last logged in users, etc
ls
| Option | Desc |
| -l | List showing date, owner,… |
| -a | Shows hiddens as well |
| -lt | List sort by time |
When you do ls -l you will get:
-rw-r--r-- 1 jboss jboss 2481 Feb 25 12:43 run.conf
| file type | read/write/exe permissions for owner/group/others | # of links | owner | group | size | date | name |
| - | rw - r - - r - - | 1 | jboss | jboss | 2481 | Feb 25 12:43 | run.conf |
There are three types of access:
- read (r)
- write (w)
- execute (x)
There are three types of files:
- ordinary file (-)
- directory (d)
- symbolic link (l)
lsmod
Show status of modules loaded into kernel. It resides in /sbin
lsof
List of open files and processes that opened them. It includes disk files, ports, etc.
For the ports do:
sudo /usr/local/bin/lsof -i :80
lspci
Lists all pci hardware devices connected
ln
create a hard or soft link.
By default, every file has a single hard link that gives the file its name. When we create a hard link, we create an additional directory entry for a file. A hard link is indistinguishable from the file itself. It is helpful to imagine that files are made up of two parts: the data part containing the file's contents and the name part which holds the file's name. When we create hard links, we are actually creating additional name parts that all refer to the same data part.
(hard link) ln <origin> <new location/filename>
(soft link) ln -s <destination> <nickname>
ln -s /x/file.ext : makes a symbolic link in the current dir to file /x/file.ext
mount
mount by force when you get mount errors: sudo mount -t ntfs-3g /dev/sdb1 /media/Network -o force
The better way is to connect the device, restart the system and everything should be good.
mv
Rename or move files.
netstat
Networking information
netstat -an show which ports are listening, etc.
nmap
This utility is for network exploration or security auditing.
| nmap -p 80 localhost | tells the status of port 80 |
| sudo nmap -sT -O myip | all open ports on myip |
nohup
nohup command &
No Hangups. When a command is invoked using nohup then SIGHUP signals are ignored. User can even sign out and the process will continue to run. This will generate a nohup.out log file.
If you do not want the nohup.out log file: nohup command 2>/dev/null 1>/dev/null &
nslookup
| nslookup -q=mx yourdomain.com | check mx records |
| nslookup -debug | verbose |
pargs
Examines a process and prints related information such as arguments and environment variables, etc.
For example pargs<PID> is useful with ptree and ps.
pkill
kill a process by name or other features. pkill python.
pstree
Shows processes in a tree format. It is usually used as pstree <PID>.
ps
view processes| Command | Desc |
| ps -ef | grep 'jboss4/bin' | Filters and shows (e)very process in a (f)ull list. |
| sudo ps -Af | SunOS |
reboot
"sudo reboot" reboots the system.
read
read -p "press enter to continue"
this stops the batch file and waits for the enter key.
rm
rm removes files. To remove directories use -fr option.
removing multiple files or directories in multiple locations: find . -name "FILE-TO-FIND"-exec rm -rf {} \;
rsync
Usual command for me was rsync -avzP. At the time of this writing rsync v3 (2013) has memory issues with large number of files. My QNAP NAS restarts during the operation with out of memory error.
scp
Remote copy: scp local_file usrname@remote_host:remote_file. If using Windows as the client, it is easier to use WinSCP. scp local_file usrname@remote_host: will copy the local_file into the home folder or user "usrname". Notice the colon. If you want to copy to the remote machine without being asked for password read the section in the HowTo page.
sed
Can edit text on a stream.
id=$(eval $xxx | grep -Po '"id": ".*"' | sed 's/"id": "' | sed 's/"')
s flag is for substitution.
if we have daynight string in a file called test then command cat test| sed 's/n/y/' will replace n with y and returns dayyight.
shutdown
To shutdown or restart the system.
| shutdown -P now | shutdown now |
| shutdown -P +30 | shutdown in 30 min |
| shutdown -P 22:10 | shutdown at a specified time |
| sudo reboot | to restart the system |
source
Same as exec command but executes in the same shell without the need to create a new process.
source .bash_profile
sudo
Run commands as another user.
sudo -u jboss x.sh runs the file as a jboss user. When used without -u then it is root.
tar
| Command | Desc |
| tar xvf archive.tar | Extract from the archive file |
| tar cvf archive_name.tar dirname/ | Create a new tar archive |
| tar cvfz archive.tar.gz SOURCE | Create a gzip compressed tar archive containing everything in the directory 'SOURCE'. You can create archives with gzip,… as well. |
tail
tail -f myfile.txt -n 100 : list the last 100 lines in the file myfile.txt. and stays there to follow
top
Shows a real time view of processes, memory usage, load, CPU state, etc.
touch
Change the time of the file. It is useful for times when a changed access time will trigger another operation…
uname
Useful information about kernel, version, distribution, machine, ….
uptime
how long the system has been up for
usermod
modify a user account. Can be used to rename users. If you rename a user don't forget to change these: /etc/passwd, /etc/group, /etc/shadow and home directory.
usermod -a -G root reza : adds user reza to roots users.
users
Prints the users currently logged in to the system.
view
view filename = vi or vim
vi commands
| Command | Desc |
|---|---|
| i | Enter text entry mode (Esc to exit) |
| ZZ | Write (if there were changes), then quit |
| :wq | Write, then quit |
| :q | Quit (will only work if file has not been changed) |
| :q! | Quit without saving changes to file |
| x | Delete a character (in command mode) |
| dd | Delete a line (in command mode) |
| Esc | leave insert (text entry) mode and return to command mode |
| yy | Copy (yank) the current line |
| R | Overwrite text, press <Esc> to end |
| 6yy | Copy (yank) six lines, beginning with the current line |
| yw | Copy the current word |
| p | Put the text after the cursor position |
| P | Put the text before the cursor position |
| /text | Search forward (down) for text. Can be used when we have / in the search text! Press n or shift+n for next and previous. |
| shift-n | find next |
| ?text | Search backward (up) for text |
| :set nu | Display line numbers |
| :set nonu | Hide line numbers |
| gg | Goto start of the file |
| G | Goto end of the file |
| :n | line n; use :0 to move the beginning of the file |
| Ctrl-b | page up |
| Ctrl-f | page down |
visudo
grants sudo access to usres| reza ALL=(ALL) ALL | gives all the sudo permissions to reza |
| reza ALL=(ALL)NOPASSWD:/sbin/shutdown | asks no password from reza when running shutdown. This should be placed after above line. order matters |
which
Shows the physical location of a command for example "which ls" tell where the "ls" is located in the disk.
yum install wget
yum update
yum
yum - Yellowdog Updater Modified, is the equivalent of apt-get for RH/CentOS.
Key combinations
- Ctrl-C: Usually sends the kill signal, which terminates a process.
- Ctrl-Z: Sends the stop signal, which stops process execution immediately, without terminating. Use “fg” or “bg” after that.
- Ctrl-L: Clears the screen and works like clear command.
wc
counts the number of lines/bytes/words/characters in files. "find | wc -l" finds the number of lines in all the files of the current directory.
wget
Get a file from the network. very useful!
who
shows who is logged in.
xev
Shows a window (in X server) and sends all X server events to it. It is good for debugging keys, mouse, etc.
xmodmap
Change/view key maps
Other References
Reference
- Internet
- http://www.dzone.com/links/r/50_most_frequently_used_unix_linux_commands_with.html
- 50 most frequently used commands: http://www.dzone.com/links/r/50_most_frequently_used_unix_linux_commands_with.html
