Download CentOS 6 CD / DVD ISO

Posted on in Categories CentOS, Download of the day last updated July 11, 2011

CentOS Linux version 6 has been released. It is a community-supported operating system based on Red Hat Enterprise Linux (RHEL) version 6. CentOS Linux is considered as the most popular Linux distribution for web servers with almost 30% of all Linux servers using it.

Red Hat / CentOS Linux 5.x: Perl Performance Bug Fix Available

Posted on in Categories CentOS, GNU/Open source, High performance computing, Linux, Linux distribution, package management, RedHat/Fedora Linux last updated September 21, 2008

Perl version supplied with RHEL has bug, which will result code running at least 100 times slower than expected speed. Now, Red Hat updated perl packages that fix a performance issue. Earlier only solution was installing your own perl under /usr/local or other location. This fix will now take care of performance penalty.

dnsmasq Dns Cache Software Security Update To Fix DNS Spoofing Attacks

Posted on in Categories BIND Dns, CentOS, Debian Linux, fedora linux, Linux, Linux distribution, package management, RedHat/Fedora Linux, Security Alert last updated August 12, 2008

Red Hat has shipped a new version of its dnsmasq caching software to plug source UDP port bug. This could have made DNS spoofing attacks (CVE-2008-1447) easier. Dnsmasq is lightweight ultra fast dns cache server forwarder and DHCP server. It is designed to provide DNS and, optionally, DHCP, to a small network.

CentOS 5 Apache 2.2.3 files failing to download or corrupted download file issue

Posted on in Categories Apache, CentOS, File system, lighttpd, Linux, Storage, Tips, Troubleshooting last updated December 1, 2007

Recently, I noticed something strange about Apache 2.2.3 version running on CentOS Linux 5 64 bit version. We have centralized NFS server and all 3 web server load balanced using hardware front end (another box running LVS).

All Apache server picks up file via NFS i.e DocumentRoot is set over NFS. The small file such as 2 MB or 5 MB get downloaded correctly but large size files failed to download. Another problem was some clients reported that the file get download but cannot open due to file corruption issue.

After investigation and a little bit googling I came across the solution. You need to disable following two options:

  • EnableMMAP – This directive controls whether the httpd may use memory-mapping if it needs to read the contents of a file during delivery. By default, when the handling of a request requires access to the data within a file — for example, when delivering a server-parsed file using mod_include — Apache memory-maps the file if the OS supports it.
  • EnableSendfile – This directive controls whether httpd may use the sendfile support from the kernel to transmit file contents to the client. By default, when the handling of a request requires no access to the data within a file — for example, when delivering a static file — Apache uses sendfile to deliver the file contents without ever reading the file if the OS supports it.

However, these two directives are known to have problem with a network-mounted DocumentRoot (e.g., NFS or SMB), the kernel may be unable to serve the network file through its own cache. So just open httpd.conf on all boxes and changes the following:
EnableMMAP off
EnableSendfile off

Just restart the web server and voila!
# service httpd restart

Lighttpd / Apache : Run Xcache in Chrooted Jail

Posted on in Categories CentOS, Debian Linux, Gentoo Linux, Howto, lighttpd, Linux, php, RedHat/Fedora Linux last updated November 26, 2007

Recently I wrote about installing and running Xcache under Red hat enterprise Linux and CentOS Linux. By default Xcache use /dev/zero for caching. All you have to do is create /dev/zero in chrooted jail. Type the following command (assuming that your jail is located at /lighttpd.jail directory):
# mkdir -p /lighttpd.jail/dev
# mknod -m 666 /lighttpd.jail/dev/zero c 1 5

Just restart your web server and xcache should work under chrooted lighttpd web server.