How to create a symlink in the Linux command console?
ln -s <destination> <linkname>
If the desired link filename is the same as the destination's filename, and the current working directory is the desired location for the link, then you only need:
ln -s <destination>
A symbolic link (also symlink or soft link) is a special type of file that contains a reference to another file or directory in the form of an absolute or relative path and that affects pathname resolution. Symbolic links were already present by 1978 in mini-computer operating systems from DEC and Data General's RDOS.
Today they are supported by the POSIX operating-system standard, most Unix-like operating systems such as FreeBSD, GNU/Linux, and Mac OS X, and also Windows operating systems such as Windows Vista, Windows 7 and to some degree in Windows 2000 and Windows XP.Symbolic links operate transparently for most operations: programs which read or write to files named by a symbolic link will behave as if operating directly on the target file. However, programs that need to handle symbolic links specially (e.g., backup utilities) may identify and manipulate them directly.
How to Open rar file or Extract rar files under Linux or UNIX
RAR files are in compressed archive format, if you have downloaded rar files from the Internet, you need to unpack or unrar them (extract rar files).RAR is a proprietary file format for data compression and archiving, developed by Eugene Roshal.Under Linux and UNIX, use command called unrar. By default unrar is not being installed on Linux, FreeBSD or UNIX oses. You can install unrar command with the help of apt-get or yum command.
Install unrar command
Under Debian Linux, you need to type apt-get as follows to install unrar program:
# apt-get install unrar
If you are using Fedora core Linux then use yum command as follows (see discussion below):
# yum install unrar
If you are using FreeBSD, use:
# pkg_add -v -r unrar
If any of above, methods is not working for you, download binary package from official rarlab site:
$ cd /tmp
$ wget http://www.rarlab.com/rar/rarlinux-3.6.0.tar.gz
Untar file
$ tar -zxvf rarlinux-3.6.0.tar.gz
Both unrar and rar commands are located in rar sub-directory. Just go to rar directory:
$ cd rar
$ ./unrar
Now copy rar and unrar to /bin directory:
# cp rar unrar /bin
How to use unrar
unrar command supports various options below are common options that you need to use everyday.
Task: To open rar (unpack) file in current directory type command:
$ unrar e file.rar
Please note that replace file.rar filename with your actual filename.
Task: List (l) file inside rar archive:
$ unrar l file.rar
Task: To extract (x) files with full path type command:
$ unrar x file.rar
(D) To test (t) integrity of archive, file type command:
$ unrar t file.rar
How to Copy, move, rename, and remove files in Linux
< Copying >
To copy files, you use the cp command. The following will copy file to file2. Note that if file2 doesn't exist, it'll be created, but if it exists, it'll be overwritten:
$ cp file file2
There aren't any undo commands in the Linux CLI, so accidentally overwriting an important file would probably make you pull your head off. The risk of doing so is smaller if you use the -i option ("interactive") with cp. The following does the same as the above, but if file2 exists, you'll be prompted before overwriting:
$ cp -i file file2
cp: overwrite `file2'? n
$
So it's a good idea to use the -i option whenever you're dealing with important files you don't want to lose!
If you want to copy file into directory dir1:
$ cp file dir1
The following would do the same as the above, copy file into dir1, but under a different name:
$ cp file dir1/file2
You can also copy multiple files into one directory with a single command:
$ cp file1 file2 file3 dir1
Note that if the last argument isn't a directory name, you'll get an error message complaining about it.
< Moving and renaming >
The mv command can be used for moving or renaming files. To rename a file, you can use it like this:
$ mv file file2
If file2 doesn't exist, it'll be created, but if it exists, it'll be overwritten. If you want to be prompted before overwriting files, you can use the -i option the same way as with cp:
$ mv -i file file2
mv: overwrite `file2'? y
$
To move the file into another directory:
$ mv file dir1
If you want to rename the file to file2 and move it into another directory, you probably already figured out the command:
$ mv file dir1/file2
< Removing files >
The rm command is used for removing files and directories. To remove a file:
$ rm file
If you use the -i option, you'll be prompted before removing the file:
$ rm -i file
You can also delete more files at once:
rm file1 file2
Be careful with the rm command! As I already told you, Linux doesn't have any undo commands, and it doesn't put files into Trash where you can save them later. Once you've deleted a file.
Ubuntu, fedora, centos, linux
How to determine which sevices are enabled at boot time in linux
How do I find out which services are enabled at Boot under Ubuntu/CentOS/RHEL/Fedora Linux? How can I disable a service which is not needed or I dont want to run every time the linux machine starts?
Open terminal and login as root user.
Type the following command to list all services which are enabled at boot:
#chkconfig --list | grep $(runlevel | awk '{ print $2}'):on
Sample output:
acpid 0:off 1:off 2:off 3:on 4:on 5:on 6:off anacron 0:off 1:off 2:on 3:on 4:on 5:on 6:off atd 0:off 1:off 2:off 3:on 4:on 5:on 6:off auditd 0:off 1:off 2:on 3:on 4:on 5:on 6:off cpuspeed 0:off 1:on 2:on 3:on 4:on 5:on 6:off crond 0:off 1:off 2:on 3:on 4:on 5:on 6:off dkms_autoinstaller 0:off 1:off 2:on 3:on 4:on 5:on 6:off haldaemon 0:off 1:off 2:off 3:on 4:on 5:on 6:off hidd 0:off 1:off 2:on 3:on 4:on 5:on 6:off irqbalance 0:off 1:off 2:on 3:on 4:on 5:on 6:off kudzu 0:off 1:off 2:off 3:on 4:on 5:on 6:off lighttpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off lm_sensors 0:off 1:off 2:on 3:on 4:on 5:on 6:off lvm2-monitor 0:off 1:on 2:on 3:on 4:on 5:on 6:off mcstrans 0:off 1:off 2:on 3:on 4:on 5:on 6:off mdmonitor 0:off 1:off 2:on 3:on 4:on 5:on 6:off messagebus 0:off 1:off 2:off 3:on 4:on 5:on 6:off microcode_ctl 0:off 1:off 2:on 3:on 4:on 5:on 6:off mysqld 0:off 1:off 2:on 3:on 4:on 5:on 6:off named 0:off 1:off 2:on 3:on 4:on 5:on 6:off netfs 0:off 1:off 2:off 3:on 4:on 5:on 6:off network 0:off 1:off 2:on 3:on 4:on 5:on 6:off ntpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off pcscd 0:off 1:off 2:on 3:on 4:on 5:on 6:off psacct 0:off 1:off 2:on 3:on 4:on 5:on 6:off readahead_early 0:off 1:off 2:on 3:on 4:on 5:on 6:off restorecond 0:off 1:off 2:on 3:on 4:on 5:on 6:off rhnsd 0:off 1:off 2:on 3:on 4:on 5:on 6:off rpcgssd 0:off 1:off 2:off 3:on 4:on 5:on 6:off rpcidmapd 0:off 1:off 2:off 3:on 4:on 5:on 6:off sendmail 0:off 1:off 2:on 3:on 4:on 5:on 6:off setroubleshoot 0:off 1:off 2:off 3:on 4:on 5:on 6:off smartd 0:off 1:off 2:on 3:on 4:on 5:on 6:off snmpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off xfs 0:off 1:off 2:on 3:on 4:on 5:on 6:off xinetd 0:off 1:off 2:off 3:on 4:on 5:on 6:off yum-updatesd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
The first column of above output is the name of a service which is currently enabled at boot. You need to review each service.
Task: Disable services
To stop service, enter:
# service {service-name} stop
# service vmware stop
To disable service, enter:
# chkconfig {service-name} off
# chkconfig vmware off
You may also use ntsysv command to manage all services.
A note about outdated insecure service
All of the following services must be disabled to improve server security:
- Inetd and Xinetd (inetd xinetd) - Use direct services configured via SysV and daemons.
- Telnet (telnet-server) - Use ssh
- Rlogin, Rsh, and Rcp ( rsh-server ) - Use ssh and scp.
- NIS (ypserv) : Use OpenLDAP or Fedora directory server.
- TFTP (tftp-server) : Use SFTP or SSH.
To delete all of the service enter:
# yum erase inetd xinetd ypserv tftp-server telnet-server rsh-serve
How to view or display a logfile in real time on screen in linux
How do I see the log file in real time including all incoming logs as well?
You can use the tail command in linux command line which outputs the last part of files in real time including all incoming logs to a file. So you can view the last parts of your logs file (like access logs for the server) using this in real time!
Note: you may need to login as root user to view log files.
Command
tail -f file-name command
If your log file name is /var/log/lighttpd/access.log, enter:
tail -f /var/log/lighttpd/access.log
If your php log file name is /var/log/lighttpd/scripts.log, enter
tail -f /var/log/lighttpd/scripts.log
You will get a scrolling view of the /var/log/lighttpd/scripts.log for all incoming entries on screen. To stop simply hit CTRL+C.
Ubuntu / Debian Linux: Install Monit Linux Server Monitoring Utility
How do I install monit to monitor my server under Debian / Ubuntu Linux?
Monit is a utility for managing and monitoring processes, files, directories and devices on a Debian / Ubuntu Linux server system. Here a few common uses of monit:
- Monit can start a process if it does not run
- Restart a process if it does not respond
- Stop a process if it uses to much resources etc
How do I install monit utility for monitoring services?
Type the following command as the root user:
$ sudo apt-get update $ sudo apt-get install monit
Configure monit
Open monit configuration file /etc/monit/monitrc using vi text editor or nano command in linux:
# vi /etc/monit/monitrc
OR
# nano /etc/monit/monitrc
You need to set following parameters:
set daemon 120 set logfile syslog facility log_daemon set mailserver localhost # primary mailserver set alert vivek@nixcraft.com # receive all alerts
The next step is to save and close this file. Where,
- set daemon 120 : Start monit in background as daemon and check the services at 2-minute intervals.
- set logfile syslog facility log_daemon : Log messages in /var/log/messsages file
- set mailserver localhost : Send email alert via localmail server such as sendmail. Set list of mailservers for alert delivery. Multiple servers may be specified using comma separator. By default monit uses port 25 - it is possible to override it with the PORT option.
- set alert vivek@nixcraft.com : You can set the alert recipients here, which will receive the alert for each service. The event alerts may be restricted using the list.
Now open /etc/default/monit file to turn on monit service:
# vi /etc/default/monit
OR
# nano /etc/default/monit
Set startup to 1, so monit can start:
startup=1
Save and close the file.
Start the monit Linux monitor tool / service:
# /etc/init.d/monit start
How to Stop/Restart Lighttpd Web Server in Debian / Ubuntu / FreeBSD linux
/etc/init.d/lighttpd is a script under Linux to stop / restart lighttpd web server.
To stop lighttpd:
Use the following command to stop lighttpd:
# /etc/init.d/lighttpd stop
To restart lighttpd:
Just type the following command to restart lighttpd:
# /etc/init.d/lighttpd restart
To start lighttpd:
# /etc/init.d/lighttpd start
Debian / Ubuntu Linux Start lighttpd
# /etc/init.d/lighttpd start
Debian / Ubuntu Linux - Stop lighttpd
# /etc/init.d/lighttpd stop
Debian / Ubuntu Linux - Restart lighttpd
# /etc/init.d/lighttpd restart
FreeBSD Start lighttpd web server
# /usr/local/etc/rc.d/lighttpd start
FreeBSD - Stop lighttpd webserver
# /usr/local/etc/rc.d/lighttpd stop
FreeBSD - Restart lighttpd webserver
# /usr/local/etc/rc.d/lighttpd restart
In case if you don't have init script, type the following:
# killall lighttpd
Ubuntu Linux Start / Restart / Stop Apache 2.2 Web Server
Q. How to restart or stop Apache 2.2 web server under Ubuntu Linux?
Task: Start Apache 2.2 Server
# /etc/init.d/apache2 start
or
$ sudo /etc/init.d/apache2 start
Task: Restart Apache 2.2 Server
# /etc/init.d/apache2 restart
or
$ sudo /etc/init.d/apache2 restart
Task: Stop Apache 2.2 Server
# /etc/init.d/apache2 stop
or
$ sudo /etc/init.d/apache2 stop
How to install webmin on your Linux web server (Redhat Fedora Caldera Mandrake SuSE MSC)
Installing webmin on your linux webserver is easy. With webmin, you can use ispconfig which is a web hosting script that you can use to host many website in one server.
Webmin website: http://www.webmin.com/
Since I have fedora I can install like this:
(this tutorial is suitable for Redhat, SuSE, Caldera, Mandrake or MSC Linux, 13M)
Login to your shell, i will be using ssh so i send this command:
wget http://prdownloads.sourceforge.net/webadmin/webmin-1.350-1.noarch.rpm
Once it has finished downloadin i send this command:
rpm -U webmin-1.350-1.noarch.rpm
(make sure to use upper case U above)
The rest of the install will be done automatically to the directory /usr/libexec/webmin, the administration username set to root and the password to your current root password. You should now be able to login to Webmin at the URL http://localhost:10000/ .
Webmin install complete. You can now login to https://hostname.domain:10000/
as root with your root password.
NOTE: the default login and password is your root and root password. this is the same login you used with you ssh to your server or whatever your root password is, so your login will be like this:
Username: root
Password: xxxx (what ever your root password is)
Install istat On a CentOS Linux to Monitor Server from iPhone or Touch
The istat application is a monitoring application that can be used to obtain basic Linux server information from your iPhone or iPod Touch phone. This application has the ability to monitor CPU Usage, Memory Usage, Disk Usage, CPU Load, and Server Uptime among many others.
To install istat on CentOS Linux follow the directions below.
- Download istat: Download istat for Linux here.
- Configure istat: Unpack the istat package you downloaded from Google Code and change the directory into the newly created istat directory. Once in this directory type the below command to configure istat for your server.
-
./configure
-
- Install istat: Now issue the make and make install commands to compile and install istat on your server.
-
make
-
make install
-
- Create istat User: Now issue the below command to create a istat user to run istat.
-
useradd istat
-
- Create istat Directory: Use the below syntax to create a directory to store the istat.pid file which needs to be readable/writeable by the istat user you just created.
-
mkdir /var/run/istat
-
chown istat.istat /var/run/istat
-
- Configure istat: Now make necessary configuration changes to the /usr/local/etc/istat.conf configuration file. The typical changes include modifying the server_code which is the access code used by your iDevice to obtain the server information, monitor_net which is the interface istat will listen for incoming connections, and monitor_disk which needs to be changed to the proper mounts such as /dev/hdb1, /dev/hdc1, etc.
- Launch istat: Now launch the istat daemon by issuing the below command.
-
/usr/local/bin/istatd &
The server will automatically launch with the istat user and listen on port 5109.
-
- Connect From iPhone: Now configure the new server within istat on your iPod Touch or iPhone. Once you do so click on the server, type in the password you set in step 6, and verify you are collecting all of the server statistics properly.
The istat application is a nifty little application to provide you a quick view of servers on your network or servers that you monitor outside of your network. More information about the iPhone version of istat can be located here.