Changing the SSH Port Number
To change the SSH port number login as root, and edit /etc/ssh/sshd_config
Find the line that says Port 22 and change 22 to any number between 1024->65535 (above 30000 is best) and save the file.
Once done, run:
Now start a new SSH session (don’t close your existing one), to make sure that you can get in.
-p port
Port to connect to on the remote host. This can be specified on a per-host basis in the configuration file.
Using netstat to find largest number of established connections
To find out the largest number of established connections you can simply use something like
netstat -an | grep ‘ESTABLISHED’ | awk ‘{print $4}’ | cut -d: -f1 | uniq -c | sort -rn | head -n 1
3 192.168.1.2
To see the list of the top 10
netstat -an | grep ‘ESTABLISHED’ | awk ‘{print $4}’ | cut -d: -f1 | uniq -c | sort -rn | head -n 10
2 192.168.1.2
How to view all
netstat -an | grep ‘ESTABLISHED’ | awk ‘{print $4}’ | cut -d: -f1 | uniq -c | sort -rn
3 192.168.1.2
You can also view all but have pages so you can view each in detail
netstat -an | grep ‘ESTABLISHED’ | awk ‘{print $4}’ | cut -d: -f1 | uniq -c | sort -rn | more
8 192.168.1.2
You can show the port with:
netstat -an | grep ‘ESTABLISHED’ | awk ‘{print $4}’ | uniq -c | sort -rn
1 192.168.1.2:58632
1 192.168.1.2:58631
1 192.168.1.2:58629
1 192.168.1.2:58628
1 192.168.1.2:58627
1 192.168.1.2:58613
1 192.168.1.2:55154
1 192.168.1.2:48673
Limit the number of Rails applications in Cpanel Server
You can limit the number of Rails applications your customers can install.
To do this in WHM, go to Modify an Account, click the domain name you wish to limit, and in the Max Mongrel Instances (Ruby on Rails) box, specify the desired maximum number of applications.
Using cat command to number nonempty output lines
-b, –number-nonblank
number nonempty output lines
root@dell:/etc# cat -b inittab
1 # /etc/inittab: init(8) configuration.
2 # $Id: inittab,v 1.91 2002/01/25 13:35:21 miquels Exp $
3 # The default runlevel.
4 id:2:initdefault:
-n, –number
number all output lines
root@dell:/etc# cat -n inittab
1 # /etc/inittab: init(8) configuration.
2 # $Id: inittab,v 1.91 2002/01/25 13:35:21 miquels Exp $
3
4 # The default runlevel.
5 id:2:initdefault:
major and minor device number
Linux creates special files, called nodes, for each device on the system. All communication with the device is performed through the device node. Each node has a unique number pair that identifies it to the Linux kernel. The number pair includes a major and a minor device number. Similar devices are grouped into the same major device number. The minor device number is used to identify a specific device within the major device group. This is an example of a few device files on a Linux server:
root@dell:/dev# ls -al sda* ttyS*
brw-rw—- 1 root disk 8, 0 Feb 8 07:12 sda
brw-rw—- 1 root disk 8, 1 Feb 8 07:12 sda1
brw-rw—- 1 root disk 8, 2 Feb 8 07:12 sda2
crw-rw—- 1 root dialout 4, 64 Feb 8 07:12 ttyS0
crw-rw—- 1 root dialout 4, 65 Feb 8 07:12 ttyS1
crw-rw—- 1 root dialout 4, 66 Feb 8 07:12 ttyS2
crw-rw—- 1 root dialout 4, 67 Feb 8 07:12 ttyS3
The fifth column is the major device node number. Notice that all of the sda devices have the same major device node, 8, while all of the ttyS devices use 4. The sixth column is the minor device node number. Each device within a major number has its own unique minor device node number.
The first column indicates the permissions for the device file. The first character of the permissions indicates the type of file. Notice that the SCSI hard drive files are all marked as block (b) device, while the COM port device files are marked as character (c) devices.
