Category: Linux

Create a file /root/fw.stop with the following content:

#!/bin/sh
echo "Stopping firewall and allowing everyone..."
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT

Make it executable and then run it on the terminal.

Source: http://www.cyberciti.biz/tips/linux-iptables-how-to-flush-all-rules.html

From time to time you may be interested in verifying that your cron jobs run as expected. How do we do that? By reading the logs of course. I will describe how to find cron logs in this article.

By default cron jobs get logged to

/var/log/syslog

To view only cron jobs, run the following command:

 grep CRON /var/log/syslog

Sometimes you may receive email failure messages when your computer tries to send a mail to a linux user regarding things like errors in cron jobs, etc. and the email address is not a valid one , e.g. root@your-computer-name. To fix this, set up forwarding of emails or aliases for your linux users. Here are the steps to setting up aliases, assuming we want to do this for the user root.

• Open the aliases file :
  $ sudo vim /etc/aliases
• Enter the new alias you want on a new line in the following format
  root: youremail@address.com
• Save and close the file
• Run the newaliases command
  $ newaliases

Now that this is done, the computer will send all root’s future emails to youremail@address.com

I describe here how to uncompress .7z files in linux, specifically Ubuntu.

1. Install p7zip – a command line port of the 7zip utility for Unix, Mac OS X, BeOS and Amiga – if not already installed by running the following command

$ sudo apt-get install p7zip

2. Uncompress the file using the command

$ p7zip -d my-file-name

Here I describe a technique to type special characters in Ubuntu with the keyboard if you use a few special symbols occasionally.

• First, learn the hexadecimal value for the character. One way to do this is to open the Character Map application, find the character and check the unicode value at the bottom of the window. Close Character Map when done. Assuming the character you want to type is é then unicode values is 00e9
• Type Ctrl + Shift + U, then type the unicode value of the character. You may omit leading zeros. So for é that will be Ctrl + Shift + U + e9. Then press Enter. Note after pressing Ctrl + Shift + U, an underlined u will appear behind the cursor to signify you are in unicode entry mode.

In order to list users on linux, run the following code

$ cat /etc/passwd

This tutorial describes how to mount a Windows partition on Ubuntu if you find it isn’t mounted automatically. We will use the UUID of the partition in mounting. I will describe how to mount Windows partition whenever Ubuntu is booted.

1. Find the device you want to mount. To do this, run the following in a terminal

$ sudo fdisk -l

Windows partitions will usually be in ntfs format. Usually it is at /dev/sda2 or /dev/sda3 and you may be able to differentiate the windows partition from a windows recovery partition by comparing the sizes.

2. Find the UUID of the windows partition by running the following in the terminal:

$ sudo blkid

Find the one corresponding to the Windows partition and have it handy.

3. Back up your file systems table configuration file (fstab) by running the following the following in a terminal:

$ sudo cp /etc/fstab /etc/fstab.orig

4. Edit fstab using your favourite editor. e.g.

$ sudo gedit /etc/fstab

5. Assuming we want to set the mount point for Windows to /media/windows, add the following line to fstab

$ UUID=the-uuid /media/windows ntfs-3g defaults,user,locale=en_US.utf8 0 0

Where the-uuid is the UUID you found in step 2. Save the close the file.

6. create that directory by running :

$ sudo mkdir /media/windows/

7. Unmount the partition and remount it by running these in a terminal:

$ sudo umount /media/windows
$ sudo mount /media/windows

Reference:
MountingWindowsPartitions – Community Ubuntu Documentation https://help.ubuntu.com/community/MountingWindowsPartitions

This post describes how to enable pinging on your amazon ec2 server.

• Log in to amazon aws console and click ec2 tab
• Find the security group  of your ec2 instance under Security Groups on the wc2 page
• Create a key and certificate which you will use with ec2-authorize command.
  • On the top right of the screen click the down arrow next to your name
  • Click Security Credentials on the dropdown menu. You will be redirected to Security Credentials page
  • Click X.509 Certicates tab under Access Credentials section
  • Click Create a new Certificate
  • Download the private key and certificate in the resulting dialog that appears
• Upload the private key and certificate to your ec2 server by sftp
• Install ec2-api-tools package if not already installed
  • To do this, enable ubuntu multiverse repository if not already enabled
    • To do this, back up your sources list by running

      $sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup 

    • Open /etc/apt/sources.list
    • Uncomment the lines for multiverse list by removing the leading # symbols
    • Save and close the file
    • Retrieve updated package lists by running

      $sudo apt-get update

• Enable icmp ping by running

  $ec2-authorize -K /path/to/private/key \
  -C /path/to/certificate your-instance-security-group \
  -P icmp -t -1:-1 -s 0.0.0.0/0