Linux Beginner Commands

arp:

Used for checking existing Ethernet connectivity and IP address
This command should be used in conjunction with the ifconfig and route commands. It is mostly useful for me to check a network card and get the IP address quick.

df:
Display filesystem information
df -h
show how much hard disk space you have on each mounted file system.

du:
Display usage
Most common use, under a specific directory: du -a

find:
Find locations of files/directories quickly across entire filesystem
Most common use: find / -name filename -type d -xdev (replace the word filename with the name of a file or application)

ifconfig:
Command line tool to configure or check all network cards/interfaces

init:
Allows you to change the server bootup on a specific runlevel

joe or nano
Easy to use command line editors that are often included with the major Linux flavors
Most common uses:joe filename nano filename

netstat:
Show the summary of network connections and status of sockets
Most common uses: netstat and also netstat head and also netstat -r

Netstat command simply displays all sockets and server connections. The top few lines are usually most helpful regarding webserver administration. Therefore if you are doing basic webserver work, you can quickly read the top lines of the netstat output by including the head (pipe and head commands). Using the -r option gives you a very good look at the network routing addresses. This is directly linked to the route command.

nslookup:
Checks the domain name and IP information of a server

ping:
Sends test packets to a specified server to check if it is responding properly

This is an extremely useful command that is necessary to test network connectivity and response of servers. It creates a series of test packets of data that are then bounced to the server and back giving an indication whether the server is operating properly.
It is the first line of testing if a network failure occurs. If ping works but for instance FTP does not, then chances are that the server is configured correctly, but the FTP daemon or service is not. However, if even ping does not work there is a more significant server connectivity issue… like maybe the wires are not connected or the server is turned off! The outcome of this command is pretty much one of two things. Either it works, or you get the message destination host unreachable. It is a very fast way to check even remote servers.

ps:
Lists all existing processes on the server
Most common uses: ps and also ps -A more
The simple command will list every process associated with the specific user running on the server. This is helpful in case you run into problems and need to for instance kill a particular process that is stuck in memory. On the other hand, as a system administrator, I tend to use the -A with the more option. This will list every process running on the server one screen at a time. I use it to quickly check what others are goofing with on my servers and often find that I'm the one doing the dangerous goofing!

rm
Removes/deletes directories and files
Most common use: rm -r name (replace name with your file or directory name)
The -r option forces the command to also apply to each subdirectory within the directory. For instance if you are trying to delete the entire contents of the directory x which includes directories y and z this command will do it in one quick process. That is much more useful than trying to use the rmdir command after deleting files! Instead use the rm -r command and you will save time and effort. You may already have known this but since server administrators end up spending a lot of time making and deleting I included this tip!

route:
Lists the routing tables for your server
Most common use: route -v
This is pretty much the exact same output as the command netstat -r. You can suit yourself which you prefer to run. I tend to type netstat commands a lot more than just route and so it applies less to my situation, but who knows, maybe you are going to love and use route the most!

shred
Deletes a file securely by overwriting its contents
Most common use: shred -v filename (replace filename with your specific file)
The -v option is useful since it provides extra view of what exactly the shred tool is doing while you wait. On especially BIG files this could take a bit of time. The result is that your file is so thoroughly deleted it is very unlikely to ever be retrieved again. This is especially useful when trying to zap important server related files that may include confidential information like user names or hidden processes. It is also useful for deleting those hundreds of love notes you get from some of the users on your server, another bonus of being a server administrator. :)

sudo:
The super-user do command that allows you to run specific commands that require root access.
Most common use: sudo command (replace command with your specific one)
This command is useful when you are logged into a server and attempt a command that requires super-user or root privileges. In most cases, you can simply run the command through sudo, without having to log in as root. In fact, this is a very beneficial way to administer your server without daily use of the root login, which is potentially dangerous.Below is a simple example of the sudo capabilities:sudo cd /rootThis command allows you to change directories to the /root without having to login as root. Note that you must enter the root password once, when running a sudo command.

top:
Displays many system statistics and details regarding active processes
Most common use: top
This is a very useful system administrator tool that basically gives you a summary view of the system including number of users, memory usage, CPU usage, and active processes. Often during the course of a day when running multiple servers, one of my Xwindows workstations just displays the top command from each of the servers as a very quick check of their status and stability.

touch:
Allows you to change the timestamp on a file.
Most common use: touch filename
Using the basic touch command, as above, will simply force the current date and time upon the specified file. This is helpful, but not often used.However, another option that I've used in the past when administering servers, is to force a specific timestamp on a set of files in a directory.

traceroute:
Traces the existing network routing for a remote or local server
Most common use: traceroute hostname

w
An extension of the who command that displays details of all users currently on the server
Most common uses: w
This is a very important system admin tool I use commonly to track who is on the server and what processes they are running. It is obviously most useful when run as a superuser.
The default setting for the w command is to show the long list of process details. You can also run the command w -s to review a shorter process listing, which is helpful when you have a lot of users on the server doing a lot of things! Remember that this is different than the who command that can only display users not their processes.

who:
Tool used to monitor who is on the system and many other server related characteristics
Most common uses: who and also who -q and also who -b