The command used to modify file permissions is chmod, short for change mode of a file. You can also use Nautilus file browser to change the file permissions. I will cover the details after a little background on the file permissions. To find the permission settings for a file, issue the following command int he terminal from the directory where your file is.

ls -l
cmd output

As you can see, the first column in the output has some strange looking character sets. This set is the file permissions for that file (directory). The third column is the owner of the file (directory) and the fourth column is the default group of the file (directory). We can ignore all the other columns at this point.

In the first column, each set would be 10 character wide. The very first character is a d for a directory or just a - (hyphen) for files. After that, the next three characters are the permissions for the owners account. The order is read-write-execute. If the superuser can read the file it would display r otherwise just a -. Similarly for write and execute w and x would be displayed. The next three characters are permissions for all the other users belonging to the file group (from the fourth column in the output above). Final three characters are the permissions for everyone not part of the group. Superusers (root accounts) can always override all the settings mentioned here and none of the permissions apply to them.

Changing Permissions – The Easy Way

The easiest way, as I said, is to just change the file permissions using Nautilus but it’s time consuming if you want to change the permissions of a lot of files. Command line way may seem tedious to begin with but it’s the faster way once you know your way around. To change the permissions in Nautilus, right click on any file (directory). Go to properties and then to permissions. Change the permissions and click ok. That’s it.

Changing Permissions – The Faster Way

To change file permissions via the terminal, you can use the chmod command. To change permissions of a file, enter the following command in the terminal.

chmod ABC path/to/file

Here, ABC is a 3 digit number which is the decimal representation of the file permissions. For example, r-x means 101 in binary which translates to 5 in decimal. So, if you want everyone to have just read and execute access to files and only the owner has the write access to files then the permissions are rwx,r-x,r-x which is 111,101,101. That translates to 7,5,5 (comma is only given for clarity here). So, the command would now be,

chmod 755 path/to/file

Don’t worry if you don’t know how binary works, you will get used to it. Easiest way is add 4 for read, 2 for write and 1 for execute. So, considering the examples above, rwx = 4 + 2 + 1 = 7 and r-x = 4 + 0 + 1 = 5. You’ll get used to this. There is another way to to this, the text method (which I don’t prefer).

chmod who=permissions filename

Where Who is any from a range of letters, and each signifies who you are going to give the permission to. They are as follows:

u - The user that own the file.
g - The group the file belongs to.
o - The other users i.e. everyone else.
a - all of the above - use this instead of having to type ugo.

And then you can directly write rwx in front of the equal sign. For example,

chmod g=rx

Next post will cover setting default permissions to files you create using umasks.

To change the hostname in Ubuntu, follow these simple steps:

1. Find out your existing hostname by entering this command in terminal:

hostname

So on my computer, the hostname is “santhosh-desktop”

2. Change the hostname by editing:

sudo nano /etc/hostname

You will see the existing hostname. Change it to whatever new hostname you want and save it by hitting Ctrl + O

In this tutorial, I change it to

gigacore-desktop

3. Now edit the hosts:

sudo nano /etc/hosts

Here change the ::1 and 127.0.1.1 to the new hostname you chose.

::1 gigacore-desktop localhost6.localdomain6 localhost6
127.0.1.1 gigacore-desktop

3. Restart the hostname service.

sudo /etc/init.d/hostname restart

Now check the hostname by following the step 1 and you should see the new hostname.

Often times Linux users find themselves wanting more from the network manager, especially laptop users on the move find it difficult to manage all the different networks they have access to. WiCD is one of the best tools for people wanting more. It’s gtk based network configuration tool, especially meant for wireless networks written in python. Apart from being dependent on gtk, it does not require any of gnome components to work. Rejoice all the openbox and fluxbox users.

Here’s what WiCD can do (taken from the official documentation),

1. Compatible with standard *nix networking commands (iwconfig, ifconfig, etc)
2. Once configured, will connect even if the X display does not start
3. Can be managed and configured via the command line using wicd-curses
4. Support for wired networks, as well as named profiles to save multiple wired configurations.
5. Supports configuring static IP addresses and DHCP on a per network basis
6. Store different static IPs, gateways, subnet masks, DNS server addresses per network
7. Automatically connect at boot – no user intervention required, even for encrypted networks
8. Keeps network keys in root accesible only (600) files (unencrypted, however)
9. Encryption (template based)
   1. WPA 1/2
   2. WEP
   3. LEAP
   4. TTLS
   5. EAP
   6. PEAP
10. Automatically connects at resume from suspend
11. Displays information about the network
12. Ability to run scripts before/after connecting/disconnecting

All this and it’s really easy to use. Let’s start by installing WiCD, if you are an Ubuntu user, you can install WiCD very easily. All you need to do is open a terminal and issue following command,

sudo apt-get install wicd

This will install both WiCD with all the required dependencies. It will then ask you for the users you want to configure WiCD for. WiCD also comes with a tray icon. You can add it by right clicking a panel and choosing add to panel option then choose custom application launcher. Give it any name you want and in the command box type,

/usr/bin/wicd-gtk

and you will have a tray icon now. Open WiCD and you will be greeted with a screen showing all the wireless networks in the range. You can then chose to connect to any network you want. If the network is protected by any security then you would have to chose the method of security in place and enter the correct key to connect to the network.

WiCD Networks

You, of course, also get the option to chose whether to use DHCP or static IPs, which DNS you want to use, which secondary DNS you want to use. gateways, subnet masks. You can also use it to manage wired networks.

WiCD Advanced

And there’s more…

WiCD Advanced 2.0

I for one have never had any problems with WiCD., although there are people who report certain incidents, it’s free from most major bugs and is a very solid program. One of my favourite distributions, Zenwalk, comes with WiCD pre-installed. Rest assured, this is a great tool to manage all your moving connection needs.

Enter the following in your terminal:

sudo dpkg-reconfigure -plow phpmyadmin

Reinstall database for phpmyadmin: Select “No”

Web server to reconfigure automatically: Select “apache 2″

It should world now. If not, do the following to include the phpMyadmin-shipped Apache configuration into Apache:

sudo ln -s /etc/phpmyadmin/apache.conf /etc/apache2/conf.d/phpmyadmin.conf

Restart apache:

sudo /etc/init.d/apache2 restart

That’s it. Let me if you have any doubts in the comment.

Say hello APG.

It stands for Automated Password Generator. And as name suggests it is tool used to generate random passwords. APG houses two password generation algorithms. One is the Pronounceable Password Generation Algorithm (default) and the other is the Random Character Password Generation Algorithm. While the first generates strong passwords that are easy enough to remember since it provides you some clues on how to remember it, the latter just generates random passwords.

Installing APG

APG is literally available for any *NIX based operating system. In this tutorial, I will tell you how to install it on Ubuntu / Debian and Fedora / CentOS linux operating systems.

In Ubuntu:

In your terminal -

sudo apt-get install apg

In Fedora:

yum install apg

Using APG

Using APG is really simple. Let’s begin with simple password generation that is easy to remember and pronounceable, which is default. It will generated 6 passwords by using the random keyboard data you provide.

In your terminal,

apg

APG will then prompt you to input some random data so that it can generate a password for you (eg. I like noob2geek.com). Do remember that these passwords will be generated randomly no matter who many times you provide the same keyboard input. So passwords won’t be the same every time. And as you can see the bracket, it provides a pronounceable clue to remember them.

OkBazCag4 (Ok-Baz-Cag-FOUR)
TabOgUt6 (Tab-Og-Ut-SIX)
novtarsEst7 (nov-tars-Est-SEVEN)
bowebcojCal5 (bow-eb-coj-Cal-FIVE)
AbrIbgan2 (Abr-Ib-gan-TWO)
eikkotVis0 (eik-kot-Vis-ZERO)

Now to generate random passwords that are not pronounceable, you need to use the -a 1 option. Where -a is the Algorithm and 1 selects random mode.

apg -a 1

This do not require any random keyboard inputs.

%l?b`m^,
OS6}C>kwZn
RI9]VZ.Hk
/1}mYh5)
[>b/s~1:Y
'*aST9"bZ

And finally to create a password that is really strong, really long (upto 63 characters) and really hard to break it, you need to make use of more options.

apg -s -a 1 -m 63 -n 4

This actually prompts you to enter some random inputs, but just hit "ENTER" key again to output the password.

}_B^kA#!c[g*8utG8"3S|2aHfP(~I_n|r8KEn"Uxq,[wtoSDYNx{K,0q:cXD619
lkSPcTbsP:>_AfQQP-gM)pI"6LXp-8}E0S*B[@jCY(6.X0j]%^9H`NN8e,,X&TH
bG05%ZF4n*ayxl-Rj5~6tV~zqPk6>d+c]_WCS4&sr7Eeq7!n?M2LpXUqjl7/[P.
B^U&@EqJpke6y`h7J?,CK#’Q!%u-`NkwDg5.Wm3ny@rYlii,>%Y0′+’g>!lki8i

This is really hard to remember as well, if you can, you got to be supernatural. To view all APG options, type man apg in your terminal.

You can install vsftpd on Ubuntu / Debian, CentOS /Fedora and RHEL linux.

Installing vsftpd on Ubuntu or Debian

sudo apt-get install vsftpd

Installing vsftpd on CentOS / Fedora

yum install vsftpd

How to configure vsftpd:

Now that you’ve installed vsftpd, follow this procedure to configure it. These steps applies for both the linux variants.

Before you get started, stop the vsftpd by typing:

service vsftpd stop

Edit the vsftp.conf

In Ubuntu / Debian:

vi /etc/vsftpd.conf

In Red Hat / CentOS

vi /etc/vsftpd/vsftpd.conf

Make the following changes:

We don’t want anonymous login:

anonymous_enable=NO

Enable local users:

local_enable=YES

The ftpuser should be able to write data:

write_enable=YES

Port 20 need to turned off, makes vsftpd run less privileged:

connect_from_port_20=NO

Chroot everyone:

chroot_local_user=YES

set umask to 022 to make sure that all the files (644) and folders (755) you upload get the proper permissions.

local_umask=022

Now that basic configuration is complete, now let us begin with locking / securing a directory to user.

sudo useradd -d /var/www/path/to/your/dir -s /usr/sbin/nologin ftpuser

Setup a password for the user:

sudo passwd ftpuser

In order to enable the ftpuser read and write the data in your home dir, change the permission and take ownership:

sudo chown -R ftpuser /var/www/path/to/your/dir
sudo chmod 775 /var/www/path/to/your/dir

Create userlist file and add the user:

Ubuntu / Debian:
vi /etc/vsftpd.userlist

CentOS / Fedora

vi /etc/vsftpd/vsftpd.userlist

and add the user:

ftpuser

save the file and open the vsftp.conf file again:

vi /etc/vsftpd.conf

Add the following lines at the end of the file and save it:

# the list of users to give access
userlist_file=/etc/vsftpd.userlist

# this list is on
userlist_enable=YES

# It is not a list of users to deny ftp access
userlist_deny=NO

After completing all these procedures it is almost ready to use it, give it a try but you will get a 500 OOPS permission denied error. To fix it you need to add a nologin to the shell set.

vi /etc/shells

The file should look like this:

/bin/ksh
/usr/bin/rc
/usr/bin/tcsh
/bin/tcsh
/usr/bin/esh
/bin/dash
/bin/bash
/bin/rbash

Add this line at the end:

/usr/sbin/nologin

Now create a usergroup and add the ftpuser to it:

sudo addgroup ftpusers
sudo usermod -Gftpusers ftpuser

Now start the vsftpd:

service vsftpd start

That’s it. Now you have a secure installation of vsftpd on your server.

All you need to do is to login as a root or make use of sudo. Open the terminal or login to your VPS and perform these commands:

To start MySQL:

sudo /etc/init.d/mysql start

To stop MySQL:

sudo /etc/init.d/mysql stop

To restart MySQL:

sudo /etc/init.d/mysql restart

SysRq

It doesn’t happen quite often but when it does – it’s a pain in the… Nevermind that, I am of course talking about system freezes on Linux. Freezes are rare but if you are like us and install, use and test beta versions of software or operating systems themselves, there is a significant chance you will end up with system crashes, freezes, kernel panics. Most people have no idea that hitting the power button is not the only option. You are likely to compromise the filesystem integrity by doing so. This is where the SysRq key comes in.

Chances are, the kernel you are using has been compiled with a flag CONFIG_MAGIC_SYSRQ when compiled. If it is – you can breathe easy because this enables you to reboot system, recover from freezes without damaging the filesystem. You can forcibly unmount file systems, kill processes, recover keyboard state, and write unwritten data to disk.

The combination is Alt, SysRq key and a third key which changes with each command. If you don’t have a separate PrtScr and SysRq keys then most probably this won’t work for you as only a screenshot would be generated. To avoid this Print Screen feature the magic SysRq combination should include the Ctrl, becoming ‘Ctrl’+'Alt’+'SysRq’+key. Some common key-binding are given below.

• ‘k’ – Kills all the process running on the current virtual console.
• ‘s’ – This will attempt to sync all the mounted file system.
• ‘b’ – Immediately reboot the system, without unmounting partitions or syncing.
• ‘e’ – Sends SIGTERM to all process except init.
• ‘m’ – Output current memory information to the console.
• ‘i’ – Send the SIGKILL signal to all processes except init
• ‘r’ – Switch the keyboard from raw mode (the mode used by programs such as X11), to XLATE mode.
• ‘s’ – sync all mounted file system.
• ‘t’ – Output a list of current tasks and their information to the console.
• ‘u’ – Remount all mounted filesystems in readonly mode.
• ‘o’ – Shutdown the system immediately.
• ‘p’ – Print the current registers and flags to the console.
• ‘0-9’ – Sets the console log level, controlling which kernel messages will be printed to your console.
• ‘f’ – Will call oom_kill to kill process which takes more memory.
• ‘h’ – Used to display the help. But any other keys than the above listed will print help.

You can also access this feature from the command line directly (as root, of course) by following command,

echo b > /proc/sysrq-trigger

This is similar to pressing the combination of Alt+SysRq+b which reboots the system. There are some cases when you want to disable this feature. You can do so with,

echo 0 > /proc/sys/kernel/sysrq

On newer kernels (exact version unknown), it is possible to have a more fine-grained control. On these machines, the number written to /proc/sys/kernel/sysrq can be zero, one, or a number greater than one which is a bitmap indicating which features to allow.

Possible values are:

• 0 – disable sysrq
• 1 – enable sysrq completely
• >1 – bitmask of enabled sysrq functions:
  • 2 – control of console logging level
  • 4 – control of keyboard (SAK, unraw)
  • 8 – debugging dumps of processes etc.
  • 16 – sync command
  • 32 – remount read-only
  • 64 – signalling of processes (term, kill, oom-kill)
  • 128 – reboot/poweroff
  • 256 – nicing of all RT tasks

Finally – in order to perform a safe reboot when you are frozen or stuck at a point. The command is unraw, terminate, kill, sync, unmount, reboot.

UPDATE – You can also use ‘i’ instead of ‘k’ in the sequence mentioned above. It does not kill the init process. Also – an easier way to remember this sequence is busier in reverse order. Remember the reverse order or you would end up rebooting the system which is useless for this purpose.

All you need to do is to login as a root or make use of sudo. Open the terminal or login to your VPS and perform these commands:

To start apache web server:

sudo /etc/init.d/apache2 start

To stop apache web server:

sudo /etc/init.d/apache2 stop

To restart apache web server:

sudo /etc/init.d/apache2 restart

Unity is developed to make day-to-day work easier on Netbooks. Since netbooks have small screens with relatively smaller resolutions, this interface is tailored to fit your applications, windows and other instances with easy access. You get to experience it’s level of user-friendliness as you start using it on your netbook. On a regular desktop or a laptop with large screen and higher resolutions, you don’t feel much of a difference but you can still install this nifty interface to either try it out or use it on regular basis for fun or for curiosity.

If you want to try out this interface, you don’t need to have a netbook or even download the Ubuntu Netbook edition. All you need to have is a computer running Ubuntu 10.10. Just follow the simple instructions and you will be good to go!

Run this in your terminal:

sudo apt-get install ubuntu-netbook

or

sudo apt-get install unity

The download size is small, but it takes few minutes to install and configure the environment.

After everything is done, you must logout of the current session and at the login screen you must select “Ubuntu Netbook Edition” at bottom and login.

To know more and see more screenshots, visit the official Ubuntu Unity page.

FYI: Unity desktop environment will be the default shell instead of Gnome shell in the upcoming Ubuntu 11.04! Having said that, don’t get into conclusion that Ubuntu is no more shipping its distro with Gnome. Ubuntu will continue with Gnome environment but only the shell will be replaced with Unity.