Entries Tagged 'Basic stuff' ↓

Finding the compiler version in your Unix system should be the first step before you attempt to compile any package from its source codes. In fact, if you're familiar with the common compilation routine, the configure script which you run to generate the Makefile before compiling anything does exactly that – it finds out which compilers (if any) you have installed on your system, and confirms their versions and capabilities.

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Now and then I come across a situation when I need to run a script or a Unix command and would like to not only see the output of it on the screen, but also save this output to some log file. Redirecting the standard output using standard Unix stream redirection isn't always useful because your output will either be shown to you, or sent to the file – but not both at the same time

tee command

That's where the tee command becomes really useful. You pipe your output to this command, and let it take care of the rest.

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visudo is a tool for safely updating the /etc/sudoers file, found in most Linux systems (Ubuntu for example).

Here's what the Ubuntu man page says about it, I think it's a great summary:

visudo edits the sudoers file in a safe fashion, analogous to vipw(8). visudo locks the sudoers file against multiple simultaneous edits, provides basic sanity checks, and checks for parse errors. If the sudoers file is currently being edited you will receive a message to try again later.

Attention: due to the sensitive content of the /etc/sudoers file, you can only run visudo as root.

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If you ever need to save the history of your Unix shell session, one of the easiest ways to do it is to use the script command, found in most Unix systems.

Simply provide the file name for your log as a command line parameter:

$ script /tmp/unix-session.log

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In Unix systems, there are 6 file types. Below I will give a very short description of each.

How to find out the type of file in Unix

The first and most obvious way to confirm the type of a particular file is to use the long-format output of ls command, invoked by the -l option:

$ ls -l * 
 -rw-r--r-- 1 greys greys       1024 Mar 29 06:31 text

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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.

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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.

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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.

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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)

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