If you’re a really curious mind, you won’t be satisfied with simply knowing the current release of your RedHat Linux, that’s why there’s a few more commands you could use to satisfy your interest.

RedHat release

If you simply want to confirm whether you’re using a RHEL4, RHEL5 or any of the previous RedHat Linux releases, this is the first place to look:

bash-3.1$ cat /etc/redhat-release
Red Hat Enterprise Linux Client release 5 (Tikanga)

RedHat kernel version and type

Next step is to find out the exact Linux kernel version on your system, and also confirm whether it’s 64-bit or not:

bash-3.1$ uname -a
Linux rhserver123 2.6.18-8.el5 #1 SMP Fri Jan 26 14:15:14 EST 2007 x86_64 x86_64 x86_64 GNU/Linux

RedHat kernel build

For the most curious ones, here’s the last command. Use it to confirm who and when compiled the RedHat kernel you’re using, and what gcc compiler was used in the build process.

bash-3.1$ cat /proc/version
Linux version 2.6.18-8.el5 ([email protected]) (gcc version 4.1.1 20070105 (Red Hat 4.1.1-52)) #1 SMP Fri Jan 26 14:15:14 EST 2007

See also

• How To Find Out the Release Version of Your Unix
• Check Raspbian version

Mounting an ISO image of a CD/DVD before burning it is one of the basic steps to verifying you’re going to get exactly the desired result. It’s also a neat trick to access files from a CD/DVD image when you only need a file or two and not a whole CD. Why burn it at all when you can access files much quicker and easier by simply mounting the ISO image?

Every Unix OS has a way to access ISO filesystem, and today I’ll only give you examples for Linux and Solaris. In both cases, the two things you need for the example to work are the ISO image itself and an available mount point (basically, an empty directory) on your filesystem to mount it under.

Here’s how to mount an ISO in Linux:

# mount -o loop /net/server/linux-bootcd.iso /mnt

Here’s how to mount an ISO in Solaris:

First, you need to associate your ISO image with a virtual device:

# lofiadm -a /net/server/linux-bootcd.iso

lofiadm approach allows you to have virtual devices associated with as many ISO images as you like, and you can view the list of current associations at any moment:

# lofiadm
Block Device File
/dev/lofi/1 /net/server/linux-bootcd.iso

To mount a virtual device, you use the following command:

# mount -F hsfs /dev/lofi/1 /mnt

See Also

• Creating bootable ISO in MacOS
• Useful options for mount and umount

If you run your Ubuntu system behind a firewall and have to use proxy server for http and ftp access, then your apt-get on a newly installed Ubuntu system will probably not work.

To make it use proxy, simply set the http_proxy environment variable. Once you get it working (try something like apt-get update), you’ll probably want to add it to your .bashrc file.

Setting the http_proxy variable

Here’s how you set the variable:

bash$ export http_proxy=http://proxy:8080

If you’re required to use your username and password for your proxy, they can be specified this way. Obviously, port 8080 can and should be replaced with the valid port for your proxy server (sometimes it’s 3128):

bash$ export http_proxy=http://username:password@proxy:8080

See Also

• apt in Linux
• List installed packages on your Ubuntu Linux

I’ve recently upgraded Apache and PHP on my VPS, and one of the unpleasant surprises was that some scripts which tried including pages from remote sites (I know, not the most secure approach, but there were reasons for that) got broken.

allow_url_fopen

Traditionally, all the websites Google finds suggest that you double-check that your php.ini config has the allow_url_fopen enabled:

allow_url_fopen = On

Well, in my case it was enabled, but scripts were still broken. The really weird thing was that the upgrade procedure didn’t include changing the php.ini in any way, so it was fully working before and I kind of expected it to continue working.

allow_url_include

After some quick research, I’ve found out that PHP 5.1 introduced a new security option to accompany the allow_url_fope, and this was exactly the option which broke my scripts:

allow_url_include = On

There you have it, hope it helps you next time you come across this problem!

If you have used your fresh Ubuntu install for longer than half an hour, chances are that you’ve discovered the sudo command already.

sudo allows certain users to execute a command under another user’s privileges. Most commonly, using sudo implies running a command as a superuser, but the approach works equally well for allowing you to inherit a user ID (uid) and group ID (gid) of any user on the system.

To gain access, a password is asked, and by default it is your password, and not the password of a user you’re trying to run a command as. This allows for the system’ s administrator to effectively manage user privileges without having any user share their password.

sudo is based off the /etc/sudoers file, which should be edited by root employing the visudo command. WARNING: although /etc/sudoers file is a regular text which root can edit manually, ONLY visudo way of updating it is recommended, as this command, apart from editing capabilities, also does a syntax check of the changes before applying them to prevent user privilege related disasters.

If you want to grant superuser privileges to a particular user, the following line should be added to the /etc/sudoers file (just type visudo to invoke the editor):

greys ALL=(ALL) ALL

In this example, greys is the username.

Related books

If you want to learn more, here’s a great book:

Starting with RHEL4, the system only accepts local (socket-based) X11 server connections. This means that if you go to another Unix server and try forwarding X11 output by using DISPLAY variable to point to your RHEL4 box, it will no longer work.

Enabling TCP connections to X11

In order to make your RHEL4 system accept TCP connections for X11, here’s what you need to do:

In /etc/X11/gdm/gdm.conf, uncomment the

#DisallowTCP=true

line and change it to

DisallowTCP=false

That’s it! Restart gdm and enjoy!

Different UNIX-like operating systems store information about their release versions differently. If you know what OS you have, but not sure about the version, then here’s how you can find out:

RedHat Linux

bash-3.1$ cat /etc/redhat-release
Red Hat Enterprise Linux Client release 5 (Tikanga)

Ubuntu Linux

bash-3.1$ cat /etc/issue
Ubuntu 6.10 n l

SUSE Linux

~> cat /etc/SuSE-release
SUSE Linux Enterprise Desktop 10 (x86_64)
VERSION = 10

Sun Solaris

bash-2.03$ cat /etc/release Solaris 8 2/04 s28s_hw4wos_05a SPARC Copyright 2004 Sun Microsystems, Inc. All Rights Reserved. Assembled 08 January 2004

See Also

• cat command
• check Raspbian version