Linux Mail Server Setup and Howto Guide » System Administration

File Management in RHEL/CentOS 5

consultant — Sun, 29 Aug 2010 13:35:55 +0000

This article describes how to manage your files in Red Hat Enterprise Linux 5 or CentOS 5.

File Management (GUI)

Managing files in GUI mode is a simple as launching the File Browser.

1. Click Applications, select System Tools then click File Browser. This will launch the File Browser window.

2. From the File Browser tool you can now perform your desired file operation.

File Management (Console)

Below are the console commands to manage files. This is just an overview of the commands available, to get more information, type in man command to get the manual for the specified command.

Common Operations

cp -a source dest
copy the specified file or directory
rm -rf name
delete the specified file or directory and all of its contents
mv old new
move a file or directory to a new location. Also used to rename a file or directory
ln -s source linkname
create a symbolic link to the specified file or directory

Directory Operations

cd
change to the home directory
cd path
change to the specified directory
pwd
print working directory
ls
list directory
mkdir name
create the specified directory
rmdir name
delete the specified directory. Directory should be empty

File Operations

chown owner file
change the file owner to the specified user
chmod permissions files
change the file permissions
cat name
shows the file content
more name
shows the file content a few screens at a time
less name
shows the file content similar to how vi displays a file
vi name
edit the specified file. Learn how to use the vi editor
head name
shows the first few lines of a file
tail name
shows the last few lines of a file

Configure Network Device in RHEL/CentOS 5

consultant — Sun, 29 Aug 2010 07:56:59 +0000

Red Hat Enterprise Linux 5 and its derivative CentOS 5, includes tools to configure the network device. This article describes how to configure network devices in Red Hat Enterprise Linux or CentOS 5.

Configure Network Device (GUI)

This section describes how to configure the network device using GUI tools.

1. Click System, select Administration then click Network. This will launch the Network Configuration window.

2. Select the network device you want to modify and click Edit.

3. In the Ethernet Device window, apply your changes and click OK.

4. Click the DNS tab and apply your DNS settings.

5. To save your changes, click the File and click Save.

6. To effect your changes, click the Devices tab. Next, select the device and click Deactivate then click Activate to reactivate the device.

7. Update your /etc/hosts file.

Although the Network Configuration tool has a feature to update the /etc/hosts file, it is more reliable to edit it directly instead.

Configure Network Device (TUI)

This section describes how to configure the network device using text user interface (TUI) tools.

1. Launch the Network Configuration TUI tool using the command below. Then apply the necessary changes to your network device.

system-config-network-tui

2. To effect your changes, restart the network service using the command below.

service network restart

3. Update your /etc/hosts file.

Configure Host Name Lookup in RHEL/CentOS 5

consultant — Sun, 08 Aug 2010 01:15:37 +0000

Before starting to use Red Hat Enterprise Linux 5 or CentOS 5, the static host name table lookup file /etc/hosts must be corrected first. The steps below describes how to do this.

Configure Hosts

1. Click Applications, select System Tools then click File Browser. This will launch the File Browser window.

2. In the Location field, type in /etc and press Enter. If you don’t see the Location field, click the notepad button to toggle to text-based location bar.

3. Locate and double click on the file hosts to open it for editing. Update the content similar to the lines below.

127.0.0.1       localhost.localdomain localhost
::1             localhost6.localdomain6 localhost6
192.168.0.4     mail.acme.local mail

Replace the last line with your own IP address, fully qualified domain name and host name.

Test the Host Name Lookup

1. Click Applications, select Accessories, and click Terminal. This will launch the Terminal window.

2. In the terminal window, type in the command below.

ping localhost

You should see localhost.localdomain and 127.0.0.1

3. Next, type in the command below.

ping mail

Replace mail with your own hostname. You should see your fully qualified domain name and ip address.

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Synchronize System Clock in RHEL/CentOS 5

consultant — Sat, 24 Oct 2009 05:05:27 +0000

Services in Linux like cron and kerberos relies on an accurate and synchronized clock. This article describes how to synchronize the system clock with an NTP server.

Configure NTP (GUI)

This section describes how to configure the NTP using the Date & Time GUI tool.

1. Click System, select Administration and click Date & Time.

2. In the Date/Time Properties window, click the Network Time Protocol tab.

3. Check Enable Network Time Protocol. Next click Show advanced options and check Synchronize system clock before starting service. Finally, click OK.

Configure NTP (Console)

Listed below are the commands to configure the NTP. You need to have root level access to use the commands below.

/usr/sbin/ntpdate pool.ntp.org
immediately synchronizes the system clock. Make sure the ntpd service is not running before using this command.
/sbin/service ntpd start
starts the ntpd service
/sbin/service ntpd stop
stops the ntpd service
/etc/ntp.conf
the above is not a command, it is the location of the ntpd configuration file

How to Setup User Password Expiration in RHEL/CentOS 5

consultant — Wed, 05 Aug 2009 14:33:57 +0000

Ideally, passwords should be changed regularly. This article describes how to setup password expiration using the User Manager application in Red Hat Enterprise Linux 5 or CentOS 5.

1. Click Applications then select System Settings and click Users and Groups. This will launch the User Manager window.

2. Select the user you wish to configure and click Properties.

3. In the User Properties windows, click the Password Info tab.

4. Check the Enable Password Expiration checkbox to enable password expiration. The list below describes the available settings.

Days before change allowed
Number of days from the last password change to allow another password change.
Days before change required
Number of days from the last password change to require another password change.
Days warning before change
Number of days before the expiry of the password to notify the user.
Days before account inactive
Number of inactive days after the expiry of the password to deactivate the account. 0 means do not deactivate.

You can also do this from the command line, below are the equivalent commands.

chage login_name
modifies the password expiry information of the specified login name. You need root access to use this command.
chage -l login_name
shows the password expiry information of the specified login name
chage
displays the help information

You can notify the users with expiring password via email using the checkpwexpire script. Copy the script into the /etc/cron.daily and give it execute permission so it will automatically run every day.

System Administration Howto

consultant — Wed, 22 Jul 2009 14:07:13 +0000

This article contains useful links on how to administer a Red Hat Enterprise Linux 5 or CentOS 5 server.

System Management

This section describes how to perform system management tasks.

How to manage directories and files

How to add, edit or remove a user account

How to add or remove packages or applications

How to start, stop or restart a background service
How to enable or disable an on demand service

How to configure a network device

How to configure the firewall

How to synchronize the system clock using NTP

System Utilities

This section describes utilities you can use to manage your system.

How to setup SSH to remotely administer a Linux server using a command line

How to use VNC to remotely administer a Linux server using a GUI

How to setup Webmin, a web based system administration tool

How to use rsync to synchronize files between two computers

How to use vi, a command line editor

How to Add the RPMforge Repository in RHEL/CentOS 5

consultant — Fri, 12 Jun 2009 14:51:21 +0000

RPMforge is a third party RPM repository for Red Hat Enterprise Linux or CentOS. Adding the RPMforge repository will give you access to an extensive library of precompiled binaries. This article describes how to add the RPMforge repository in Red Hat Enterprise Linux or CentOS 5.

Adding RPMforge to Yum

The rpmforge repo package can be downloaded from the site below.

1. Launch Firefox and go to http://dag.wieers.com/rpm/FAQ.php#B2. Click on the package appropriate for your version of Red Hat Enterprise Linux or CentOS.

2. Choose Open with Software Installer (default) and click Ok.

3. The Installing packages window will appear. Click Apply to proceed.

4. Finally click Ok.

Lowering the RPMforge priority

Lowering the priority of the RPMforge repository will ensure that the base packages provided by RHEL/CentOS will not be replaced by a newer version from RPMforge.

1. Install the Yum priorities package using the command below.

yum install yum-priorities

2. Edit the file /etc/yum.repos.d/rpmforge.repo and add the line below.

priority=10

3. Test your configuration using the command below. You should see a priority protections message in the output.

yum check-update

Rsync Howto

consultant — Tue, 19 Aug 2008 09:04:39 +0000

Rsync is a software that synchronizes files and directories using a small amount of data transfers. You can use this to backup data. This page will show you how to use rsync to synchronize files from a source machine.

For Windows users, you can use DeltaCopy. DeltaCopy includes the rsync console application and a client and server GUI.

Server

1. Edit the file /etc/rsyncd.conf and add the lines below.

[pub]
path=/home/public
read only=no

Replace pub with any directory name you prefer. The path on the other hand should point to a valid nobody readable and writeable directory.

2. Allow the rsync service to launch by enabling it in the On Demand Service in the Service Configuration tool. Learn more about the Service Configuration tool.

3. Open the rsync port 873 in the firewall. Learn how to configure the firewall.

Client

To transfer a file/directory, the basic command is rsync src dest. Below are some examples.

To get a file/directory from the server, type in

rsync rsync://server/pub/test.txt .

Replace server with the name of your server, pub with the name of your directory, test.txt with the name of a file or directory you wish to download and replace . with a path to your local directory if you do not want to save into your current directory.

To send a file/directory to the server, type in

rsync test.txt rsync://server/pub

Replace server with the name of your server, pub with the name of your directory, test.txt with the name of a file or directory you wish to upload.

Webmin Setup Howto

consultant — Wed, 28 May 2008 13:47:49 +0000

Webmin is a web-based interface for system administration for Unix. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more. This article will show you how to install Webmin.

1. Go to www.webmin.com and download the Webmin RPM package.

2. Double click the downloaded file to install Webmin.

3. After installing Webmin, configure the firewall to allow traffic on the TCP port 10000. Learn how to configure the firewall.

4. Start the httpd service. Learn how to start and stop services here.

5. From a web browser, connect to https://localhost:10000 and login using root.

6. That’s it. It’s working.

VNC Remote Desktop Howto

consultant — Sat, 26 Apr 2008 23:14:13 +0000

Virtual Network Computing (VNC) is a graphical desktop sharing system which enables you to remotely control another computer. This article will show you how to setup VNC server to remotely manage your Linux machine.

VNC server should already be included in a Server GUI installation, but if you chose a custom installation, you can install it using the Package Manager tool.

VNC Server

The VNC server should be configured from a remote SSH terminal.

1. Launch the VNC server by typing in vncserver in an SSH window. If this your first time to run vncserver, you will be asked for a password. VNC server will show your hostname followed by a colon and a number. Note down this number.

To change your VNC password, type in vncpasswd in a terminal window.

2. Type in vi ~/.vnc/xstartup to edit the xstartup file. Note that .vnc is a hidden directory. Uncomment the lines below

unset SESSION_MANAGER
exec /etc/X11/xinit/xinitrc

and replace

twm &

with either “startx &” for a GNOME desktop or “startkde &” for a KDE desktop.

Check out the vi Editor Tutorial if you need help in using vi.

3. Terminate your VNC session by typing in vncserver kill :1 Replace 1 with the number from step 1. Then launch it again using the command from step 1. You need to discard the session before xstartup was modified, otherwise you will be working on a remote desktop session built from the stone age.

VNC Client

To connect to the remote VNC server, we will be using TightVNC, a free remote control software package derived from the popular VNC software.

1. Launch TightVNC. The New TightVNC Connection window will be shown. Fill in the VNC server field and click Connect. The VNC server field has the format hostname:number. Number is the session number noted down from step 1 of VNC Server.

2. In the Standard VNC Authentication window, type in your VNC password.

3. That’s it, you now have a remote desktop session using VNC.