How to update grub boot loader config

GRUB boot loader starts up what's necessary for your Linux or UNIX system to boot up. You can edit its settings, like various boot options and which operating systems to select from, by editing the the /boot/grub/grub.cfg or /etc/grub.conf depending on your system. Graphical programs are also available for this purpose. See our GRUB Boot Loader overview for more.

Once you've edited your configuration you'll need to update grub to use it. This is very easily done by this single command:

sudo update-grub

Then once you reboot your new config should be active.

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Ubuntu: How To Enable SSH

Secure Shell (SSH) allows secure communication between networked computers for such purposes as logging in to a remote computer, running some commands remotely, and transferring files (with the scp command).

By default SSH is not enabled in Ubuntu. There is an ssh command installed, but it is only a client, and only allows you to login into another computer, not to allow others to login into yours.

To enable that you first need to install the OpenSSH Server. To do that just use apt-get:

sudo apt-get install openssh-server

If you prefer you can also search for openssh server in the Ubuntu Software Center and install it that way.

Once it is installed you need to enable it in the OpenSSH Server configuration. To do this open and edit the /etc/ssh/ssh_config file with superuser privileges:

sudo nano /etc/ssh/ssh_config

The nano program is a terminal based text editor, but if you prefer a graphical editor you can open it in gedit:

$ sudo gedit /etc/ssh/ssh_config

In that configuration file look for the Port 22 line and uncomment it by removing the preceding hash sign #. That's all you need to edit to get the SSH server working, but if you wish you can review, enable, and edit other configuration options.

Once you're done save the file and restart SSH (which was started automatically when openssh-server was installed) for changes to take effect:

sudo service ssh restart

… or using the old method:

$ sudo /etc/init.d/ssh restart

Your Ubuntu machine will now be able to accept SSH logins and communications through its IP address or host domain.

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How To Mount DMG Files from Command Line in Mac OS

DMG files are proprietary disk image files used for software distribution in Mac OS. Providiing both password protection and bzip2-like compression, these files are perfect packaging medium.

Usually DMG files are opened automatically when you click them in Finder. They appear as a folder with files, but actually Finder mounts each DMG file as a separate filesystem and then shows you its contents. If you're observant enough, you'll see that in the left side panell of Finder you have all the active DMG filesystems listed and ready to be ejected once you finish copying the files or installing new software.

Sometimes you may want to download and mount DMG file using Mac OS command line, and in this post I'll show you how to do it

[Read more...]

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How To: Use yum behind proxy

I've got a few RedHat and CentOS VMs running on internal network of my server, and since updating them quite regularly is a habit I thought this little piece of advice will help all of you who run VMs in a similar scenario.

To make yum command use proxy, your best best is to edit /etc/yum.conf and add your proxy server reference:

proxy=http://192.168.3.1:3128

You don't have to restart anything but it may be a good idea to do yum clean all and then yum check-update:

[root@testvm1 ~]# yum check-update
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: be.mirror.eurid.eu
* epel: epel.uni-oldenburg.de
* extras: be.mirror.eurid.eu
* updates: centosa5-msync-dvd.centos.org
base                                         | 3.7 kB 00:00
base/primary_db                              | 4.5 MB 00:01
cr                                           | 3.0 kB 00:00
cr/primary_db                                | 1.2 kB 00:00
epel                                         | 3.4 kB 00:00
epel/primary_db                              | 3.7 MB 00:00
extras                                       | 3.5 kB 00:00
extras/primary_db                            | 6.3 kB 00:00
updates                                      | 3.5 kB 00:00
updates/primary_db                           | 1.8 MB 00:01

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Upgrading Ubuntu with do-release-upgrade

There comes a time (a couple of times a year, actually) when you may want to upgrade your Ubuntu distro (read here for instructions on confirming your version of Linux: Find Out Linux Version)

Once that's done, you can use do-release-upgrade for a hassle free upgrade.

IMPORTANT: are you can see, I've used a really old Ubuntu server with 8.10, hence your procedure for upgrading more recent Ubuntu versions may be slightly different. For example, later upgrades will warn you if you're doing a release upgrade over ssh.

What do-release-upgrade is and when you should use it

do-release-script is a Python script which automates the process of updating multiple packages. It relies upon Ubuntu's core package management functionality.

Apart from downloading and installing updated versions of packages found on your system, this command attempts to take care of all the necessary Ubuntu-release related file changes.

Step 1: Run do-release-upgrade

Once you type the do-release-upgrade command name and press Enter, you should see how vital information about packages currently installed is being collected:

# do-release-upgrade
Checking for a new ubuntu release Done
Upgrade tool signature Done
Upgrade tool Done
downloading
extracting 'jaunty.tar.gz'
authenticate 'jaunty.tar.gz' against 'jaunty.tar.gz.gpg'
Reading cache
Checking package manager
Reading package lists: Done
Reading state information: Done
Updating repository information
Done http://archive.ubuntu.com jaunty Release.gpg
Done http://archive.ubuntu.com jaunty-updates Release.gpg
Done http://security.ubuntu.com jaunty-security Release.gpg
Done http://us.archive.ubuntu.com jaunty-backports Release.gpg
Done http://security.ubuntu.com jaunty-security Release

Checking package manager
Reading package lists: Done
jaunty-security/multiverse
Packages: 98  2
Reading state information: Done
Reading state information: Done
Reading state information: Done
Calculating the changes

 

2. Confirming what upgrading will do

This is your last change to change your mind. All the necessary information about your current Ubuntu release is collected, and now you're presented with the exact upgrade details: how many packages will be removed, how many new ones will be installed, how many will be upgraded. You also are given details about the required amount of data to be downloaded should you decide to proceed with the upgrade;

Do you want to start the upgrade?

1 package is going to be removed. 23 new packages are going to be installed. 420 packages are going to be upgraded.

You have to download a total of 248M. This download will take about 7 minutes with your connection.

Fetching and installing the upgrade can take several hours. Once the download has finished, the process cannot be cancelled.

Continue [yN]  Details [d]

Ready? Press y for yes!

3. Downloading all the packages

Just like with apt-get, you will now see the progress of downloading all the updated packages for your Ubuntu OS. At the bottom of the screen you will see the overall completeness of the download (22% in my example), the current download speed (598kB/s in my case) and the ETA:

Done http://archive.ubuntu.com jaunty-updates/main libbz2-1.0 1.0.5-1ubuntu1.1
Done http://archive.ubuntu.com jaunty/main libdb4.7 4.7.25-6ubuntu1
Done http://archive.ubuntu.com jaunty/main libncursesw5 5.7+20090207-1ubuntu1
Done http://archive.ubuntu.com jaunty-updates/main libssl-dev 0.9.8g-15ubuntu3.6
Done http://archive.ubuntu.com jaunty-updates/main libssl0.9.8 0.9.8g-15ubuntu3.6
Done http://archive.ubuntu.com jaunty/main python2.6 2.6.2-0ubuntu1
[23%] 598kB/s 5min17s

4. Upgrade

Once package are downloaded, they will get installed once by one, with package-specific questions asked for software like postfix or apache.

5. Reboot

To finalize the distro upgrade, you will need to do a reboot. Once completed, you should have a shine next release available.

Recommended books:

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Fixed calculations in Unix scripts

Although I've already shown you how to sum numbers up in bash, I only covered the bash way of doing it. I really like scripting with bash, but when it comes to calculations, there's quite a few important features missing from bash, and fixed point (thanks for the correction, Azrael Tod!) calculations is one of them. Fortunately, bc command comes as a standard in most Unix distros, and can be used for quite complex calculations.

Basic calculations with bc

bc is a very simple command. It takes standard input as an expression and then evaluates this, performing all the necessary calculations and showing you the result. Thus, to quickly sum numbers up or get a result of some other calculation, simply echo the expression and then pipe it out to the bc command:

ubuntu$ echo "1+2" | bc
3

[Read more...]

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Command Aliases in Unix shells

One of the really useful features almost every Unix shell has is support for command aliases – a way to run a command or a series of Unix commands using a shorter name you get associated with such commands.

An example of a command alias in Unix shell

Here's one of the most useful aliases I have for Solaris systems:

solaris$ alias ls='/usr/local/gnu/bin/ls --color -F'

[Read more...]

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Ubuntu SSH: How To Enable Secure Shell in Ubuntu

SSH (Secure SHell) is possibly the best way to remotely access a Unix system – it's very secure thanks to automatic encryption of all the traffic, and it's also quite universal because you can do all sorts of things: access remote command line shell, forward graphics session output, establish network tunnels, set up port redirections and even transfer files over the encrypted session.

Today I'm going to show you how to get started with SSH in Ubuntu.

Installing SSH server in Ubuntu

By default, your (desktop) system will have no SSH service enabled, which means you won't be able to connect to it remotely using SSH protocol (TCP port 22). This makes installing SSH server one of the first post-install steps on your brand new Ubuntu.

The most common SSH implementation is OpenSSH. Although there are alternative implementations (closed source solutions and binary distributions maintained by various Unix and Unix-like OS vendors), OpenSSH is a de-facto standard in the secure transfers and connections industry. That's exactly what you want to install.

[Read more...]

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How to Confirm Disks Capacity in Linux

show disk size in Unix is a very popular request visitors use to arrive at my Unix Tutorial pages. Since I never addressed the question of confirming the number of hard drivers available on your system or the task of finding out a disk's capacity, I'd like to document a quick and easy way of doing just that.

I hope that when someone looks for a way to show disk size, what's really expected is a command to help you confirm the capacity of a disk in gigabytes.

Using fdisk command in Linux

One of the easiest ways to learn a lot about hard drives installed on your Linux system is to use the fdisk command: [Read more...]

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