Fedora Linux reconfigure X server

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Q. I messed up with my X server configuration. Now I would like to reconfigure X server.

A. Fedora comes with the X Configuration Tool called redhat-config-xfree86 which provides a graphical interface for creating, modifying or reconfiguring the XFree86 configuration file.

At shell prompt type following command to reconfigure X server under Fedora Linux (login as the root user):
# redhat-config-xfree86

You can pass –reconfig option and –noui option if want to disregard any configurations on existing XFree86 configuration files. This is useful when your system is with no prior X configuration:
# redhat-config-xfree86 --reconfig --noui

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Open ftp port 21 on windows XP operating system

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MS-Windows XP service pack 2 comes with in build firewall. If Microsoft Windows Firewall is blocking a port that is used by a service or by a program, you can configure the Windows Firewall to create an exception. Windows Firewall may be blocking a program or a service if Programs do not respond to a client’s request or you do not get data from server.

Open ftp port 21
To open ftp port 21 you need to change windows firewall settings.
Click on Start > Settings > Control Panel > Click on Security center

At the bottom window (Manage security setting for:) you will see Windows Firewall option. Click on this option. It will open Windows Firewall dialog box:

Select Exception tab > Click on Add port

Add port 21 and 20 and save the firewall (see above two figures).
Save firewall by clicking on Ok button. You are done now your Windows XP box will allows incoming FTP connection. Please note that you need to run FTP server in order to establish connection.

Apache restrict access based on IP address to selected directories

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Apache web server allows server access based upon various conditions. For example you just want to restrict access to url http://payroll.nixcraft.in/ (mapped to /var/www/sub/payroll directory) from 192.168.1.0/24 network (within intranet).

Apache provides access control based on client hostname, IP address, or other characteristics of the client request using mod_access module.

Open your httpd.conf file:
# vi /etc/httpd/conf/httpd.confLocate directory section (for example/var/www/sub/payroll) and set it as follows:
<Directory /var/www/sub/payroll/>
Order allow,deny
Allow from 192.168.1.0/24
Allow from 127
</Directory>
Where,

  • Order allow,deny: The Order directive controls the default access state and the order in which Allow and Deny directives are evaluated. The (allow,deny) Allow directives are evaluated before the Deny directives. Access is denied by default. Any client which does not match an Allow directive or does match a Deny directive will be denied access to the server.
  • Allow from192.168.1.0/24: The Allow directive affects which hosts can access an area of the server (i.e. /var/www/sub/payroll/). Access is only allowed from network 192.168.1.0/24 and localhost (127.0.0.1).

Save file and restart apache web server:
# /etc/init.d/httpd restart

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Linux compliant wireless cards

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Q. I am looking to upgrade my home network with wireless networking. Is there a list of wireless card supported by Linux?

A. As you may be aware, it is a networking technology allowing the connection of computers without any wires and cables, mostly using radio technology.

These days Linux (aka kernel) supports various USB/PCI wireless cards for both Laptops and desktops systems. The best way to verify this is to contact card manufacturer / vendor. A quick search on manufactures web site will help you to get idea which card supported under Linux.

My personal experience is that cards from Intel (Centrino), Cisco, Netgear, DLink works with Linux.

There is a short list of wireless cards along with links to driver and vendor website. Make sure you visit an index of information and documentation of interest to those who now use or are considering using Linux on a notebook or laptop computer.

Linux is gaining popularity so most wireless card vendors started to include drivers on site. It may be possible that driver is not included in your running kernel, you need to get it from vendors web site. When you download driver it comes with installation instructions (look for READEM and INSTALL files).

Linux change the monitor or video card settings

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Q. I am new to Linux. While playing with Linux display setting I made few of change to monitor and video card settings and restarted the Linux computer. Now I am getting very bad display. I am not able to get back GUI tools, how do I fix this mess?

A. Linux comes with the X Configuration Tool. Sometime you play with X display and after restart it will not work or during installation you select wrong settings. Here are list of tools you can use to reset your monitor and video card display settings:

If you are using FreeBSD use following two commands:

# Xorg -configure
# XFree86 -configure

Alternatively, use sysinstall tool:

# sysinstall

If you are using Debian Linux type command:

# dpkg-reconfigure xserver-xfree86

If you are using RedHat Enterprise or Fedora Linux type command:

# redhat-config-xfree86

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Sorry too many clients when trying to connect to PostgreSQL database server – solution

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Q. I am running PostgreSQL server for my web application and I am getting an error “Sorry too many clients when trying to connect to PostgreSQL”. How do I troubleshoot this database error?

A. This error indicates that you have reached the default limit set in your configuration postgresql.conf file. Under FreeBSD default limit is 40 database session. You need to increase this level.

Please note that increasing this level costs about 500 byes of shared memory per connection slot, in addition to costs from shared_buffers and max_locks_per_transaction.

Edit file /usr/local/pgsql/data/postgresql.conf (FreeBSD) or /var/lib/pgsql/data/postgresql.conf (Red Hat Linux) or /etc/postgresql/postgresql.conf (Debian Linux):

# vi /usr/local/pgsql/data/postgresql.conf

Locate parameter max_connections and set new value. For example if you want to 300 database session, it should read as follows:

max_connections = 300

Save the file and restart postgresql server. If you are using FreeBSD restart postgresql with following command:

# /usr/local/etc/rc.d/010.pgsql.sh restart

On the other hand, if you are using Debian Linux, restart postgresql with following command:

# /etc/init.d/postgresql restart