User Tools

Site Tools


2016:nsrc-tein-lernet:ubuntu

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

2016:nsrc-tein-lernet:ubuntu [2016/02/03 05:04] (current)
Line 1: Line 1:
 +====== Ubuntu System Administration ======
 +
 +===== Notes =====
 +
 +  * Commands preceded with "​$"​ imply that you should execute the command as a general user - not as root.
 +  * Commands preceded with "#"​ imply that you should be working as root with "​sudo"​
 +  * Commands with more specific command lines (e.g. "​RTR-GW>"​ or "​mysql>"​) imply that you are executing commands on remote equipment, or within another program.
 +
 +===== Find out what's installed =====
 +
 +Log on to your machine using SSH as the user specified in class.
 +
 +Once you are logged in, take a look at all the packages installed on your system:
 +
 +  $ dpkg --get-selections
 +
 +All installed packages fly by on the screen. Let's slow that down:
 +
 +  $ dpkg --get-selections | less
 +
 +The "​less"​ command lets you quickly search text. Is the "​openssh-server"​ server
 +installed on your machines? ​ (It should be if you are logged in :)
 +
 +  Type "/​openssh"​ and press <​ENTER>​
 +
 +You should see something like:
 +
 +  openssh-client ​                                ​install
 +  openssh-server ​                                ​install
 +
 +with the "​openssh"​ text highlighted. Press "​q"​ to exit the less screen.
 +
 +Another way to see packages is:
 +
 +  dpkg --list | less
 +
 +Try it!
 +
 +What version of "​openssh-server"​ is installed?
 +
 +  $ apt-cache policy openssh-server
 +
 +Or, you could also say:
 +
 +  $ dpkg --list openssh-server
 +
 +===== Find out if a package is available to be installed =====
 +
 +You have a local cache of all packages available to be installed from the Ubuntu
 +package repositories. You can search this cache using the "​apt-cache"​ command. Before ​
 +you can use apt-cache the first time you need to update your local cache. Let's do this
 +now (we did this for you when setting up your machine):
 +
 +  $ sudo apt-get update
 +
 +Once this completes we can search for available packages. Let's see if the "​ipcalc" ​
 +package is available in our Ubuntu repositories:​
 +
 +  $ apt-cache search ipcalc ​
 +
 +It looks like there are three packages matching the name "​ipcalc"​. Try typing:
 +
 +  $ sudo apt-get install ipcalc
 +  [sudo] password for sysadm: .... <- your password
 +
 +Then try:
 +
 +  $ ipcalc 41.93.45.101/​24
 + 
 +This is very useful! We'll talk more about what all this means later today or tomorrow.
 +
 +**NOTE: If we ask you to run a command on the system and you are told it isn't available, you can use this process to install it.**
 +
 +===== Stopping and starting services =====
 +
 +The scripts to run services on your machine are located in /​etc/​init.d/​. By default,
 +when Ubuntu installs a package the startup scripts for the package are run and the
 +package is configured to automatically run at system startup.
 +
 +Try viewing the status of the ssh server, stopping and starting the server and 
 +reloading the server'​s configuration file (/​etc/​ssh/​sshd_config):​
 +
 +  $ service ssh help
 +
 +You are shown the commands you can perform on the ssh service.
 +
 +Try to view the status of the ssh server:
 +
 +  $ sudo service ssh status
 +
 +Since we are connected using ssh we cannot stop this service. If we did, then you would
 +lose your connection and need to go to your machine'​s console to manually restart the
 +service.
 +
 +===== Use the top command =====
 +
 +The top command let's us see the status of our system at a quick
 +glance. To use top simply do:
 +
 +   $ top
 + 
 +The item at the top of list of running processes is the process using
 +the most CPU resources.
 +
 +Open a new SSH connection to your PC. In that window type:
 +
 +   $ ls -lahR /
 + 
 +Now in the other window where top is running you should start to see the "​ls"​
 +process listed using some amount of your total CPU.
 +
 +At the top of the top window you'll see something like:
 +
 +  top - 03:17:03 up  1:47,  2 users, ​ load average: 0.51, 0.19, 0.09
 +  Tasks: ​ 79 total, ​  2 running, ​ 77 sleeping, ​  0 stopped, ​  0 zombie
 +  Cpu(s): ​ 4.9%us, 10.9%sy, ​ 0.0%ni, ​ 3.6%id, 79.6%wa, ​ 1.0%hi, ​ 0.0%si, ​ 0.0%st
 +  Mem:    508924k total, ​  ​491968k used,    16956k free,    59052k buffers
 +  Swap:   ​905208k total, ​    4584k used,   ​900624k free,   ​128712k cached
 +
 +This is a good, quick way to see how much RAM, Virtual memory, CPU,
 +total running processes, etc. that your machine has, and is using.
 +
 +You can adjust the output of top as it is running. Exit from top by
 +typing "​q"​ and then do:
 +
 +  $ man top
 + 
 +Now run top again and change what it is displaying interactively.
 +
 +**HINT**: You can also type **h** while running top to get quick summary of commands
 +
 +All the information in top is part of a dynamic file system located in
 +/proc. As an example do the following:
 +
 +  $ cd /proc
 +  $ ls
 +
 +The numbered directories correspond to actual Process IDs of processes
 +that are running. Look at the file meminfo:
 +
 +   $ less meminfo
 + 
 +Remember: space bar to go to the next screen of output.
 +
 +Note that it includes your total RAM. Top uses this file to get this
 +information. Same for cpuinfo, loadavg, uptime, etc.
 +
 +If you want to know what command was executed to start a number process
 +you can type (for instance):
 +
 +   $ less /​proc/​1/​cmdline
 + 
 +You'll see that the first process started on the system is init.
 +
 +===== Viewing your log files in real time =====
 +
 +In a window connected to your pc type:
 +
 +  $ sudo tail -f /​var/​log/​auth.log
 + 
 +Now open a second window to your PC and login using ssh.
 +
 +What do you see in the first window?
 +
 +In the second window try:
 +
 +  sudo -s
 +  ​
 +What do you see in the first window?
 +
 +Now go back to being the **sysadm** user by typing:
 +
 +  exit
 +
 +What do you see in the first window?
 +
 +Now close your second ssh session using:
 +
 +  exit
 +
 +What do you see in the first window?
 +
 +This method of looking at log files can be very useful if you are trying to debug problems. We'll use it later.
 +
 + 
 +
 +
  
2016/nsrc-tein-lernet/ubuntu.txt ยท Last modified: 2016/02/03 05:04 (external edit)