The Geeky Linux :: Ubuntu/Linux blog :: Open source Tips and Tricks :: Linux Howtos and Tutorials

Install aspell dictionary in linux

2015-06-13T00:59:00.001+05:30

To install "aspell" in linux, follow the below steps:

cd /usr/local/src
wget ftp://ftp.gnu.org/gnu/aspell/aspell-0.60.6.tar.gz
tar -xvzf aspell-0.60.6.tar.gz
cd aspell-0.60.6/
./configure
make
make install

This will install aspell at the location /usr/local/bin/aspell. Make sure that you have build tools installed on your operating system. If you don't, you can install it using the below command in ubuntu :

sudo apt-get install linux-headers-$(uname -r) build-essential

How to paste in putty in Ubuntu Linux

2014-12-29T19:11:00.001+05:30

The key board short cut to paste the content from clipboard to putty terminal in Linux is Ctrl+Shift+Insert

First copy the content using Ctrl+C. This will copy the content to buffer. Then go to putty terminal and press Ctrl+Shift+insert

How to dual boot Linux (CrunchBang Linux) and PC-BSD 10 with ZFS file system

2014-11-29T02:20:00.000+05:30

This is a tutorial which shows how to dual boot Linux and PC-BSD 10. PC-BSD 10 uses ZFS as the file system and grub for the boot manager. I was able to successfully dual boot PC-BSD and CrunchBang Linux in my laptop.

I was able to achieve this after lots of trial and error methods. I have not found a valid guide in the internet to do it. All the tutorials were outdated or at least not working for me. I have spend a lot of time in the pc-bsd/freebsd irc channels and finally able to achieve this after trying out different suggestions from the irc members. Thanks to them all for the guidance.

If you want to dual boot PC-BSD, first install the Linux os (in this case, CrunchBang Linux) and then install PC-BSD 10. This is because most of the Linux OS won't be able to detect ZFS (the default file system in PC-BSD 10). But PC-BSD grub will be able to detect EXT4 the default file system in most of the Linux distros. If you are looking for a tutorial for PC-BSD with UFS and Linux, you can find lot of guides in the interwebs. My guide only applies to PC-BSD with ZFS file system.

1. Install Crunch Bang Linux
2. Copy the relevant part from the Crunch Bang Linux grub menu. You can get it from the configuration file /boot/grub/grub.cfg . There will be lot of unwanted details in this menu but we will only need the one starts after the line "### BEGIN /etc/grub.d/10_linux ###" in this file .

For example, below given is the relevant part from my Crunch Bang Linux grub configuration :

menuentry 'CrunchBang GNU/Linux, with Linux 3.2.0-4-amd64' --class crunchbang --class gnu-linux --class gnu --class os {
    load_video
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos5)'
    search --no-floppy --fs-uuid --set=root 1fa97d1a-97c2-45ab-ba94-1f692ce86756
    echo    'Loading Linux 3.2.0-4-amd64 ...'
    linux    /boot/vmlinuz-3.2.0-4-amd64 root=UUID=1fa97d1a-97c2-45ab-ba94-1f692ce86756 ro quiet
    echo    'Loading initial ramdisk ...'
    initrd    /boot/initrd.img-3.2.0-4-amd64
}

And upload this to online website like http://pastie.org/ and take a note of the link. This is because we need to get this after we install PC-BSD and configuring it's grub

3. Install PC-BSD 10 with ZFS as the file system
4. You won't see any option to boot Crunch Bang Linux after you install PC-BSD
5. Once you boot to PC-BSD, edit the grub configuration for PC-BSD
Open /usr/local/etc/grub.d/40_custom and add the earlier copied Crunch Bang Linux grub configuration to this file so that it will look like this.

cat /usr/local/etc/grub.d/40_custom

menuentry 'CrunchBang GNU/Linux, with Linux 3.2.0-4-amd64' --class crunchbang --class gnu-linux --class gnu --class os {

load_video

insmod gzio

insmod part_msdos

insmod ext2

set root='(hd0,msdos5)'

search --no-floppy --fs-uuid --set=root 1fa97d1a-97c2-45ab-ba94-1f692ce86756

echo 'Loading Linux 3.2.0-4-amd64 ...'

linux /boot/vmlinuz-3.2.0-4-amd64 root=UUID=1fa97d1a-97c2-45ab-ba94-1f692ce86756 ro quiet

echo 'Loading initial ramdisk ...'

initrd /boot/initrd.img-3.2.0-4-amd64

}

5. Update the grub configuration in PC-BSD with the below command

grub-mkconfig > /boot/grub/grub.cfg

Then reboot and make sure that grub is showing the above entries.

Some times you need to do “Hold Left-Shift for menu entries” to display all the boot entries.

How to install Mozilla Thunderbird in CrunchBang Linux

2014-10-24T08:15:00.000+05:30

There is no Mozilla Thunderbird package in CrunchBang Linux. So if you try

sudo apt-get install thunderbird

it won't work. The Thunderbird is rebranded to Icedove in Debian. As CrunchBang is using Debian as upstream, it is Icedove in CrunchBang Linux also.

So we can install Thunderbird/Icedove using the below command in CrunchBang Linux and Debian.

sudo apt-get install icedove

This is as simple as it is. Hope it helps.

Install broadcom BCM43142 wireless drivers in CrunchBang Linux

2014-10-18T13:03:00.000+05:30

Below given is the steps to install BCM43142 wireless drivers in CrunchBang Linux.

sudo apt-get install linux-headers$(uname -r | grep -Po "\-[a-z].*")

sudo apt-get install build-essential dkms

If you are using 32 bit, download the below deb file and install

https://drive.google.com/file/d/0B7FT1rIUqC3ScHJMOHlTREtWX1k/view?usp=sharing

cd downloads

sudo dpkg -i wireless-bcm43142-dkms-6.20.55.19_i386.deb

If it is 64 bit,

https://drive.google.com/file/d/0B7FT1rIUqC3STjR3d0xMZGYzMW8/view?usp=sharing

cd downloads

sudo dpkg -i wireless-bcm43142-dkms-6.20.55.19_amd64.deb

Now reboot your machine and after the reboot, wireless will be working fine.

This is tested on CrunchBang Linux based on Debian 7.6 Wheezy

Credit goes to : http://askubuntu.com/questions/175104/how-do-i-install-bcm43142-wireless-drivers-for-dell-vostro-3460-3560/

How to fix " skype depends on libqtwebkit4 (>= 2.1.0~2011week13)." error in debian/crunchbang 64 bit linux

2014-08-05T03:13:00.000+05:30

I have been using skype 4.2 version in my crunchbang 64 bit. Recently Microsoft has stopped supporting this version and users are showing an error "server failed to connect" while logging in to skype.

So I have to update skype to 4.3 to fix the issue. I'm using 64 bit crunchbang and Microsoft has only 32 it deb package for debain (which is what crunchbang is based on). So I have downloaded the deb file and when installing I was getting the below error :

skype:i386 : Depends: libqtwebkit4:i386 (>= 2.1.0~2011week13) but it is not going to be installed

This is because our skype deb file is 32 bit and it depends on 32 bit libqtpwebkit4. This is how to install skype on debian/crunchbang.

First download skype from the link : http://www.skype.com/en/download-skype/skype-for-linux/downloading/?type=debian32

dpkg --add-architecture i386

apt-get -f install

apt-get install libqtwebkit4:i386

rm -rf ~/.Skype

dpkg -i skype-debian_4.3.0.37-1_i386.deb

I was able to successfully install skype 4.3 using this method. I wasn't able to find a accurate guide to install skype 4.3 in debian/crunchbang linux. So I hope this will help them install skype 4.3 in their machine.

Please let me know if it works for you in the comments.

Port forwarding port 80 of public static ip to internal machines port 8080 in centos using iptables

2013-12-08T21:03:00.000+05:30

I have a centos server acting as router. It has two ethernet ports eth0 and eth1. eth0 is configured with the public static ip got from my ISP. I have my internal machines connected to this centos os router machine using LAN in eth1.

For example, assume that my public static ip given by my ISP is 123.45.567.89 and it is configured in eth0. In eth1 my internal machines are connected through LAN. Internal machines are in the ip range of 192.168.1.0 to 192.168.1.100

I have a web application running on one of my internal machines with IP 192.168.1.10 on port 8080. I can access this web app from my internal network by typing http://192.168.1.10:8080/ in a web browser. But I want to get this application from my public static ip given by ISP by simply typing http://123.45.567.89/ in the web browser. How can I achieve this? By port forwarding. Follow the below steps to achieve this.

Enable port forwarding in linux kernel by adding the below line in sysctl

vi /etc/sysctl.conf

net.ipv4.ip_forward = 1

Then enable it by running the below command:

sysctl -p

Now create the firewall rules for port forwarding.

iptables -I FORWARD 1 -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -I FORWARD 1 -p tcp -d 123.45.567.89 --dport 80 -j ACCEPT

iptables -t nat -A PREROUTING -p tcp -d 123.45.567.89 --dport 80 -j DNAT --to-destination 192.168.1.10:8080

iptables -t nat -A POSTROUTING -j MASQUERADE

service iptables save > /etc/sysconfig/iptables

service iptables restart

Now just open the link http://123.45.567.89/ in web browser and it should open the app running on internal machine 192.168.1.10 on port 8080.

Install MTS MBLAZE 3GPLUS/MBLAZE ULTRA dongle for ZTE in Ubuntu Linux

2013-12-08T20:46:00.000+05:30

I had recently got MTS 3GPLUS dongle. It is made ZTE and really good news about it is that it supports Linux and it is mentioned in their website (you can view the supported os list in "tech spec"). I have tried it in Windows 8, OSX Mavericks and Ubuntu 13.04 and it works really well on all these platforms.

In mac and windows, it will auto configure everything for you. But in Linux, you need to install it manually. When I plugged it into my ubuntu, it was detected as USB drive but there was no auto configure for it. Even I was not able to load the installation files in Ubuntu. Then I have to plug it into another Windows and was able to see it includes the files for installing it in Linux too.

So I copied the Linux installation files in a usb and copied it to Ubuntu and manually installed it.

If you weren't able to get the installation for files for ubuntu, you can download it from this link.

Then unzip it and follow the below steps. I have unzipped it to Downloads folder and I did the below steps.

cd Downloads/ZTEMBLZAE\ for\ Linux/

chmod +x autorun.sh

sudo ./autorun.sh

Then you need to reboot your Linux machine to load the required kernel modules. Once it has been rebooted you can start the MTS app by running the below commands in the terminal.

ztemtapp

This will give you the Graphical Interface and you can click "connect" to connect to the internet.

Short review: I really liked it. It really has good internet speed and best option available in the market.

How to create a user to ssh to the server and then only have super user permission to switch to root user?

2013-11-23T12:32:00.003+05:30

I don't want to ssh to my linux server as root user. So I have disabled the direct root login through ssh. I am using a less privileged user to ssh to the server. But I don't want to give him sudo privilege. The only privileged command this user (less privileged user) should be able to run is to switch to root user. How can I achieve this?

I'm using Amazon Linux (which is actually centos based) in my ec2 instance. It comes with 'ec2-user' which has no password and but has sudo privilege and uses ssh key for login. I want to use password login for other users (and don't want to use ssh key for them)[So I can't disable password login "PasswordAuthentication no" field in sshd_config file]. But I also want to set password for 'ec2-user' as I don't want to use sudo command without password. I have used below setup to achieve this.

NOTE: While doing the below steps, please make sure that you have opened a terminal and logged in to the ec2 instance and became root. Never close this terminal or log out of root user. Do below steps by connecting to the ec2 instance using another terminal. If you have messed up any of the command, there is a chance that you will be locked out of your server permanently. I hope you understand what you are doing and I won't be responsible if you have locked out of your server. These steps are intended for advanced users and also a note to myself.

1. Log in to the ec2 instance as 'ec2-user' using ssh key and became root by running "sudo -s" command which won't prompt for password.

2. Setup password for root user using "passwd" command. Verify this password by opening another terminal and ssh to ec2 instance as root user (without ssh key)

3. Disable direct root login through ssh by changing the below line in /etc/ssh/sshd_config file

PermitRootLogin yes

to

PermitRootLogin no

Restart sshd service using the below command

/etc/init.d/sshd restart

Now try again to login as root user using password and it won't work. So we have successfully disabled ssh root login

4. Set up password for 'ec2-user' using the command "passwd ec2-user" . Run this command as root user.

Now we have set up password for 'ec2-user' and 'root' user. Verify the 'ec2-user' password by logging in to ec2 instance without ssh key in another terminal and it will prompt for ec2-user password.

5. Edit the below two files as root user and comment out below lines.

Open /etc/sudoers.d/cloud-init and comment out below line and save it

# ec2-user ALL=ALL:NOPASSWD ALL

Open /etc/sudoers file and comment out the same

# ec2-user ALL=ALL:NOPASSWD ALL

Then before saving the /etc/sudoers file, add below lines to make 'ec2-user' to give privilege to switch to root user

##Below two lines make sure that ec2-user is able to switch to root user
##but not able to run any other privileged commands
Cmnd_Alias SU=/bin/su
ec2-user ALL=SU

Save the file.

Then you can open another terminal and connect to the ec2 instance as ec2-user (without using ssh key). Then type below command to switch to root user.

su - root

Then give root user's password and you will become root.

If you try, sudo -s as ec2-user, it will show error message as 'ec2-user' is not allowed to run this command.

This will make sure that if somebody need to do any administrative task in the server, he need to have ec2-user password as well as root user password.

Hope it helps somebody.

How to delete file names with spaces older than 30 days in linux?

2013-11-23T11:48:00.000+05:30

I want to delete files which are modified before 30 days from a public folder (uploads) in my linux server. The files are uploaded by different users so it includes white spaces and other characters in the file name. How can I automate this process?

You can use any of the below commands to achieve this:

find /var/www/uploads/ -type f -mtime +30 -exec rm -f {} \;

find /var/www/uploads/ -type f -mtime +30 -delete

Both these commands will do the job for you. Then you can add it to cron job to automate this process.

While using this command, you need to be careful and take necessary precautions.There may be other system files which has not been changed during 30 days in the server. So you need to make sure that these commands will affect only a particular folder. I have purposefully omitted removing directories in the above command.

If you want to remove directories/folders also, you can omit "-type f" option. If you are using my first command, you need to change "rm -f" to "rm -rf" to remove folders. If you are using my second command, you don't need to make any changes except omitting the "-type f" option.

Also you can make necessary changes to achieve other conditions also. You may use -atime for access time, -30 for reversing the days condition (not older than 30 days) etc. Make sure that you don't use system directories to run the find command.

How to delete a user from a group using single command in linux?

2013-09-07T13:02:00.000+05:30

I have created a user called 'sam' and he is a member of the group 'webdeveloper'. Currently he is on long leave and I want to remove him from the web developer group without deleting this user. How can I do this? We will find below.

We can edit /etc/group file and remove the user 'sam' from 'webdeveloper' . But there is also another simple way by using a simple command.

Use below command to remove user 'sam' from group 'webdeveloper' without editing any files.

gpasswd -d sam webdeveloper

The general syntax is :

gpasswd -d user group

How to mount NTFS filesystem as read-writable in Mac OSX 10.8 Mountain Lion

2013-08-08T22:45:00.001+05:30

Mountain Lion has built in support for read-writable NTFS filesystem. But it is enabled as read only by Apple. This means that you can only read from an NTFS formated hard disk but cannot write data to it.

To make it is as read-writable is very easy. There is no need to install any third party half working solutions or expensive softwares. Follow below steps :

1. Open the terminal app

2. Become 'root' by typing below command and give your current user's password

sudo -s

3. Create a file called /etc/fstab (it won't be there so we need to create it). I'll use vi editor here.

vi /etc/fstab

4. Write below lines to it and save the file. Replace "My Passport" with your external hard disk's name. You can use 40 to represent space. So "My Passport" become "My40Passport"

LABEL=My40Passport none ntfs rw,auto,nobrowse

5. Now remove the external hard disk and reconnect it.

6. If it is not showing in the Finder, just open a terminal and type below command to open it.

open /Volumes/My\ Passport/

7. Now try copying some files from your Mac to this external hard disk and it should be working now.

Source : apple forums

Download and install the bleeding edge version of elementary os

2013-08-03T20:10:00.000+05:30

This post is more like a note to myself.

Elementary OS is a distro which uses ubuntu as its base os. But unlike the other ubuntu based distros it's a class apart. It uses its own custom developed applications,icons and themes and everything works as a coherent unit.

The os is still in beta as developers want to release a thoroughly tested stable version for its users.

But that didn't force you to wait for its stable release. You can try the unstable builds (which are actually pretty stable). I was using the bleeding edge version of eOS for last 6 months or so until I purchase the new laptop (in which I installed Ubuntu 13.04 with dual booting Windows 8). So this time I decided to try it in Virtual Box.

So these are the links:

Go to http://sourceforge.net/projects/elementaryos/files/unstable/

Download the latest released iso (should be the first one)

I was also using the elementary daily ppa to update my old eOS installation daily.

So once installed the latest unstable build, add the daily ppa to it.

sudo add-apt-repository ppa:elementary-os/daily

sudo apt-get update

sudo apt-get upgrade

This will keep all your installed eOS packages to bleeding edge.

If you are looking for the beta release image, please download it from here.

Warning :

Bleeding edge shouldn't be used on a production system. It is only for testing purpose and to attain our own geeky nirvana.

How to fix the "built in speaker not working" issue in laptops with Ubuntu 13.04 (UEFI)

2013-07-30T20:29:00.001+05:30

Recently I have bought a new Sony Vaio touchscreen laptop with Windows 8 UEFI boot (laptop is really good and I highly recommend it) . It was fairly easy to install Ubuntu 13.04 along side windows 8. I was successfully able to dual boot Windows 8 and Ubuntu in this laptop.

In Windows 8 as expected everything worked perfectly out of the box but it was a different story in Ubuntu. I have spent almost 3 weekends for a solution and finally found the solution from some of the old bug reports dated back to Ubuntu 8.04.

The issue was that that the laptop's built in speaker didn't work out of the box. But audio is working perfectly if we plug in a headphone. So I can confirm that the issue a just with the built in speaker audio driver with Ubuntu.

I have found so many other users are also affected by this same issue. So I have tried all the available solutions in askubuntu forums like changing the alsa module (editing /etc/modprobe.d/alsa-base.conf ) and upgrading the kernel (my kernel is 3.8.0-19-generic). Nothing worked and finally I ended up with no sound at all, even from the headset.

So I re-installed Ubuntu and fixed the issue with below solution.

It is just that update your alsa package from ubuntu audio development team. Just download the correct verion of your alsa from here , install it and then reboot your computer.

After the reboot, sound should be working from the built in speaker as well as headset. Also I can confirm that there was no issue like sound is playing from both headset and built in speaker at the same time.

So for my Ubuntu 13.04 64 bit (only 64 bit has UEFI support), I have downloaded "raring build". In terminal (CTL+ALT+T) type below commands

cd ~/Downloads/

wget https://code.launchpad.net/~ubuntu-audio-dev/+archive/alsa-daily/+files/oem-audio-hda-daily-dkms_0.201307180559~raring1_all.deb

sudo dpk -i oem-audio-hda-daily-dkms_0.201307180559~raring1_all.deb

Then reboot,

sudo init 6

After the reboot, check your sound and it should be working as it should be.

If this has helped to fix your sound issue, please let us know in the comments with the below details. This will be really helpful to other users who are also suffering from the same issue:

* * * * * * * * * * * * * * * * * * * * * * * * *

Laptop :

Sony VAIO Fit 15E F15215SN/W

Sound Card :

sudo aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC233 Analog [ALC233 Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
Subdevices: 1/1
Subdevice #0: subdevice #0

sudo lspci -v | grep -A7 -i "audio"
00:1b.0 Audio device: Intel Corporation 7 Series/C210 Series Chipset Family High Definition Audio Controller (rev 04)
    Subsystem: Sony Corporation Device 90b8
    Flags: bus master, fast devsel, latency 0, IRQ 45
    Memory at c0810000 (64-bit, non-prefetchable) [size=16K]
    Capabilities: [50] Power Management version 2
    Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
    Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
    Capabilities: [100] Virtual Channel

How to save using vim editor with sudo privilege

2013-07-12T16:10:00.001+05:30

Some times we will start editing the configuration files or the files which need root privilege in vi/vim and once we are about to save it, we will understand that we haven't edited it with sudo privilege.

It may be almost impossible to think quitting the editor without saving (:q!) and start it all over agin.

But not to worry, vi has the trick to quit the editor by saving it even if you haven't opened with sudo privilege.

So when you are in same situation, while saving use,

:w !sudo tee %

Then it will ask to type the sudo password, type the password. Now it is saved. Then you can type :q! quit it.

You can see that your changes has been saved.

Install flite (festival lite) text to speech system in linux

2013-06-27T21:11:00.002+05:30

Flite is text to speech engine for linux. It is based on festival speech synthesis system. Most of the linux sytems comes with flite in its package manager. It's just a apt-get on debian based or yum install in rpm based systems.

For example, you can install it on centos with below command:

yum install flite-devel

If it is not available in your system, you can compile and install it.

1.   Download Flite 1.3

wget http://www.speech.cs.cmu.edu/flite/packed/flite-1.3/flite-1.3-release.tar.gz

2.   Download patch to enable Flite 1.3 to build shared libraries and save it in the same directory as flite-1.3-release.tar.gz

wget http://asterisk-flite.sourceforge.net/extras/flite-1.3-sharedlibs.patch

3. Download patch to enable ALSA support for Flite 1.3 and save it in the same directory as the previous patch file

wget http://asterisk-flite.sourceforge.net/extras/flite-1.3-alsa_support.patch

4. In a terminal, go to the directory where the files were saved

   Extract flite:

    tar -xzvf flite-1.3-release.tar.gz

5. Change to the extracted flite directory:

    cd flite-1.3-release

6. Apply the patches:

    patch -p1 < ../flite-1.3-sharedlibs.patch

    patch -p1 < ../flite-1.3-alsa_support.patch

   7. Apply the patches:

    patch -p1 < ../flite-1.3-sharedlibs.patch

    patch -p1 < ../flite-1.3-alsa_support.patch

   8. Configure & compile flite:

    ./configure --enable-shared --with-audio=alsa

    make

   9. Install flite to the system:

    su -c 'make install'

Reference: http://asterisk-flite.sourceforge.net/

How to download files recursively using wget as ftp client

2013-06-23T17:29:00.000+05:30

I like to use rsync for scp for transferring files from another server whenever possible. But sometimes, we will be limited to use ftp for the same task due to different ssh port than the standard 22 as scp and rsync uses ssh.

Downloading each file separately one after another is tedious task than recursively download them. We can use wget with ftp protocol for recursively downloading files from another server. We will find out how to do this below.

We can use the below syntax for downloading file using wget recursively.

wget -r ftp://server.com/ --user username --password 'password'

Here -r make sure that files are downloaded recursively. If you want to download a specific folder and its contents recursively, change the command accordingly.

For example, to download only the blog folder of main site from remote server which is located at /home/user/public_html/blog

wget -r ftp://server.com/public_html/blog --user username --password 'password'

If we need to just download a backup file at home directory of user, there is no need for -r (recursive) switch.

wget ftp://192.168.0.1/mybackup.tar.gz --user username --password 'password'

This will download the file current working directory.

Some times some servers won't allow ftp in passive mode. Then we need to use below command with --no-passive-ftp switch

wget -r ftp://server.com/mybackup.tar.gz --user username --password 'password' --no-passive-ftp

As you see above, there is no need to use server.com, but you can use the server's resolving ip address instead and it will save some dns look ups and make the process faster, a bit faster.

How to autostart dropbox linux client daemon at server reboot

2013-06-23T17:14:00.000+05:30

We have seen the script to start dropbox linux client daemon to start automatically if it is getting killed before. But how to autostart the client at server reboot?

As usual we can add the script to cronjob to take care of this. We will find this how below.

My dropbox client is at /usr/local/src/dropbox.py. You can find your dropbox client location by running the below command:

which dropbox
/usr/local/src/dropbox.py

Now create a crontab entry to start this daemon at reboot

crontab -e
@reboot/usr/local/src/dropbox.py start

That's all. Now your dropbox client will autostart at reboot as this cron will run at after the system reboot.

Script to check whether dropbox (dropboxd daemon) is running in linux server using command line

2013-06-23T17:07:00.000+05:30

Now a days more people are using dropbox for backup in linux servers. Dropbox is a great product which has their client in all major platforms. So this is really ideal for using in linux servers too.

Dropbox runs dropboxd daemon in the server to check for updates and syncing the contents between its clients across different platforms. Sometimes this daemon will get killed and our backup process will be in jeopardy.

This is a small script which will check whether the dropbox daemon is running in linux server and if not automatically start it. Add this script to cronjobs and you are set.

The script is given below:

Create a file named /root/dropbox_checker.sh

vi /root/dropbox_checker.sh

Add below script to it.

#!/bin/bash
if /usr/local/src/dropbox.py running && [ $? -eq 0 ]; then
/usr/local/src/dropbox.py start
else
echo "dropbox is already running"
fi

Add it to cronjobs.

crontab -e

0 * * * * sh /root/dropbox_checker.sh &> /dev/null

Now this will check whether the dropbox daemon is running in every hour and if not automatically start it.

Delete all iptables rules in linux

2013-06-08T18:58:00.000+05:30

We have seen how to remove a particular IP from the iptables rule. Now what if we want to remove all the iptables rule?

We can use the below command to remove all iptables rule.

iptables --flush

If we want to remove a particular chain rule use below command:

iptables --flush 'chain name'

For example, to remove all INPUT rules use below command:

iptables --flush INPUT

Finally save it by running the below command:

/etc/init.d/iptables save

How to remove a rule from iptables

2013-06-08T17:52:00.000+05:30

I want to remove a rule from iptables which used to block one of the IPs to and from the server. How can I remove it? We will find it below.

IP which is blocked: 123.456.78.90

This will basically cut off all the tcp communication from and to my server for the IP 123.456.78.90

Now I want to remove this rule so that 123.456.78.90 can easily connect to my server.

So first I need to check which line number this rule is using below command.

iptables -vnL --line-numbers | grep 123.456.78.90

7 0 0 DROP all 123.456.78.90 0.0.0.0/0
8 0 0 DROP all 0.0.0.0/0 123.456.78.90

The first column is the line number. This is one of the key thing which we need.

Now we also need to know which 'Chain' this rule comes under. To know this I grep the IP in /etc/sysconfig/iptables file which is used to store all the iptables rules in plain text. In our example, the Chain this rule comes under is 'TDENY'

grep 123.456.78.90 /etc/sysconfig/iptables

-A TDENY -s 123.456.78.90/32 -j DROP
-A TDENY -d 123.456.78.90/32 -j DROP

The command to remove these two rules are:

iptables -D TDENY 7
iptables -D TDENY 8

The format is

iptables -D 'chain type' 'line number'

And don't forget to save your work. To save it use below command:

/etc/init.d/iptables save

How to install go language tools in ubuntu

2013-06-06T07:39:00.000+05:30

In the latest version of Ubuntu, the go language tools may be already available in the repos. In that case try,

   sudo apt-get install golang

If it is not working, add go tools PPA and install it.

   sudo add-apt-repository ppa:gophers/go

   sudo apt-get update

   sudo apt-get install golang-stable

Then create a go lang program, say helloword.go and run it to test it.

cat helloworld.go
package main

import "fmt"

func main() {
    fmt.Println("Hello World")
}
Then run it,

go run helloworld.go

If everything is okay, it will give the below output and you are good to go.

Hello World

Reference:
http://code.google.com/p/go-wiki/wiki/Ubuntu
http://golang.org/doc/install

How to run a golang program

2013-06-05T13:05:00.001+05:30

Go is a language developed at google. The golang programs are generally having the extension '.go'.

So this is how we run a golang program.

go run helloworld.go

This is the program

cat helloworld.go
package main

import "fmt"

func main() {
fmt.Println("Hello World")
}

When we execute it, we get the below output.

go run helloworld.go
Hello World

How to run bash script in debug mode

2013-06-05T12:17:00.001+05:30

Running the bash script in debug mode help us understand what is going on in the script before getting the output. This also help us find why our program didn't run if there is any issue.

It is just like step by step processing of the bash program.

We can use the below command to run the bash script in debug mode in run time.

bash -x mybashscript.sh

This is my bash script which will print 1 2 and 3 in each line

cat mybashscript.sh
#!/bin/bash

for i in {1,2,3}
do
echo $i
done

This is the output of the script (without debug mode)

./mybashscript.sh
1
2
3

This is the output when the script is run in debug mode

bash -x mybashscript.sh
+ for i in '{1,2,3}'
+ echo 1
1
+ for i in '{1,2,3}'
+ echo 2
2
+ for i in '{1,2,3}'
+ echo 3
3

How to format golang code

2013-06-05T10:51:00.002+05:30

Golang is a language developed at Google. More information can be found at the wikipedia page.

Go has an easy tool called gofmt to format the code blocks of go program in easy readable format.

Here is the command to format the golang program using gofmt and save it to the corresponding file.

gofmt -w helloworld.go

If we didn't use -w, it will write to formated code to standard output. If we use -w, it will save the formatted code to the corresponding file itself.

Before formatting:

cat helloworld.go
package main
import "fmt"
func main() {
fmt.Println("Hello World")
}

After formatting:

cat helloworld.go
package main

import "fmt"

func main() {
fmt.Println("Hello World")
}