The Linux top command provides a terminal task manager which lists all of the running processes on the computer.
I use “Top” to kill a process within the top interface simply press k and enter the process id next to the application you wish to close. Top solicits a specific signal to send; in most cases, enter 15 (to request the process to gracefully terminate) or 9 (to immediately kill the process).
The first line offers some basic high-level info about the system:
- The time
- How long the computer has been running
- Number of users
- Load average
The load average shows the system load time for the last 1, 5 and 15 minutes.
The second line summarizes the number of ongoing, concurrent tasks:
- Total number of tasks
- Number of running tasks
- Number of sleeping tasks
- Number of stopped tasks
- Number of zombie tasks
The third line summarizes CPU performance:
- usage by the user
- usage by system
- usage by low priority processes
- usage by idle processes
- usage by io wait
- usage by hardware interrupts
- usage by software interrupts
- usage by steal time
The fourth line emphasizes memory:
- Total system memory
- Free memory
- Memory used
- Buffer cache
The fifth line highlights available swap space and total memory inclusive of swap:
- Total swap available
- Total swap free
- Total swap used
- Available memory
The main table lists running processes:
- Process ID
- Nice level
- Virtual memory used by process
- Resident memory used by a process
- Shareable memory
- CPU used by process as a percentage
- Memory used by process as a percentage
- Time process has been running
Key Switches For the ‘top’ Command
Although you invoke top just by typing the name in a shell session, a few switches modify the utility’s behavior:
- -h: Show the current version
- -c: This toggles the command column between showing command and program name
- -d: Specify the delay time between refreshing the screen
- -o: Sorts by the named field
- -p: Only show processes with specified process IDs
- -u: Show only processes by the specified user
- -i: Do not show idle tasks
So what is it and why do I need to know about it?
SSH, also known as Secure Socket Shell, is a network protocol that provides administrators with a secure way to access a remote computer. SSH also refers to the suite of utilities that implement the protocol. Secure Shell provides strong authentication and secures encrypted data communications between two computers connecting over an insecure network such as the Internet. SSH is widely used by network administrators for managing systems and applications remotely, allowing them to log in to another computer over a network, execute commands and move files from one computer to another.
The encrypted keys for each computer are stored in a file /home/User/.ssh known_hosts
You will need to turn on View Hidden Files in your file explorer to see the .ssh folder and all other system folders and files.
When you look at the known_hosts file there will be a line for each computer that looks like this:
|1|guO7PbLLb5FWIpxNZHF03ESTTKg=|r002DA8L2JUYRVykUh7jcVUHeYE= ssh-rsa AAAAB3NzaC1yc2EAAFADAQABAAABAQ....etc
The problem is that the hostname is “Hashed”. This is great from a security point of view. But not so useful in a “home network scenario”.
So we need to turn off the setting “HashKnownHosts = yes” to “HashKnownHosts =no “
This setting is located at /etc/ssh ssh_config at the bottom of the file for me anyway!
After you change this setting you will need to delete the known_hosts file. You will then have to reauthorize the connection to each of your computers, again. But this time when you look at the file, there will now be an I.P. Address at the start of each line.
[192.168.1.101]:22 ssh-rsa AAAAB3NzaC1yc2EAAFADAQABAAABAQ....etc
So next time you have an error you won’t need to delete the known_hosts file but instead just edit it and delete the one line that correlates to the computer that you’re trying to connect to.
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