Friday, November 25, 2011

Add file type swap to linux

To add swap to linux machine:

1. Create a swap file. Size depends on your preference. Let's say we want to create a swap file with 8GB size (1024 x 1024 x 8 = 8388608).

# dd if=/dev/zero of=/swapfile bs=1024 count=8388608
where if is source, of is output file for dd to write to which is /swapfile in this case, bs is read/write byte size at a time and count is number of blocks.

2. Once created, make it a swap file
# mkswap /swapfile
3. Activate your swap file
# swapon /swapfile
4. Check your newly created swap space using free or top
# free -m
# top
5. To make it appear even after reboot, put it into fstab
# echo "swapfile swap swap defaults 0 0" >> /etc/fstab
It will look like this:
# cat /etc/fstab 
/swapfile1 swap swap defaults 0 0

Tuesday, November 1, 2011

ssh forward tunnel

To make this happen, the command is like below:

$ ssh -L 10022:target.local:22 middle.local
-L is for forward tunnel, 10022 is the port at localhost that we want to use, target.local is our target, 22 is the target's port that we want to forward and middle.local is our middleman server.

What the above command do is forwarding port 22 of target.local to port 10022 of localhost by using middle.local as a middleman. Once done, you can access port 22 of target.local just by SSHing into port 10022 in your localhost like below:
$ ssh localhost -p10022
and voila, you will be directed to target.local instead. This technique is useful when you have firewall blocking some ports, and you have server behind the firewall than can access those ports witth openssh installed.