Operating system
An Operating System (abbreviated as OS), is a software that is responsible to manage the system resource. An operating system contains many applications in it. Operating system is directly handle the request which are received from Hardware devices (i.e. Keyboard, Mouse, Motherboard etc.).
There are many operating systems provide GUI (Graphical User Interface) through which you can manage it and some others provide CLI (Command Line Interface). It is easy to manage the Operating system which provides GUI. For CLI operating systems, you should have strong knowledge of commands.
Now a days, most cmmonly used operating systems are Windows, Linux, Unix, Solaries, CentOS etc. Some of them are commercial version and you will need to purchase the license to use it.
Linux is the open source and hence it is freely available. However if you want enterprise edition of Linux then you will need to purchase the lincese for Commercial version.
Kevin
What is FSCK?
What is FSCK? Why is it required? There are several reasons behind the system file corruption. For example, you forgot to shut down your system properly, suddenly cut off the power supply, a storage device was removed when system is in process to write the data on it, accidentally press the restart button of your system.
In Linux some data is kept in the memory before it is written to the disk. This speeds up the process and it used in many systems including Windows OS. If the system is turned off or improperly shut down before it writes the data from memory to disk then there is a chance of the system file corruption. Hence, it is required to shut down the system properly. During improper shut down, the file systems are unmounted from the memory. FSCK will unmount these file systems during boot automatically. You can also run FSCK program manually using the below command:
To check root file system:
fsck -V -a
For all other than root file systems:
fsck -R -A -V -a
The last command will check everything except root (-R) file systems.
You can also tell fsck to show what it did using echo option as below:
fsck -A -V ; echo ==$?==
The fsck codes are listed in the below table:
Code Explanation
0 No errors
1 File system errors corrected
2 System should be rebooted
4 File system errors left uncorrected
8 Operational error
16 Usage or syntax error
128 Shared library error
Generally, fsck repairs the file systems automatically. If it fails to repair the file systems then you probably have a corrupted superblock.
Kailash Aghera
Host table on Linux server
In the beginning, the host table was the only tool to map the host name to IP address. All Linux systems still have a host table, which is located at “/etc/hosts” file. The host table contains the IP addresses and host names. Below is the sample example of the hosts file:
$ cat /etc/hosts
# Table of IP addresses and host names
127.0.0.1 localhost
165.2.3.5 myserver
All the lines in the host table have same format. Lines begin with the IP address and it followed by a list of names that map to that IP address. Using above host table when a user specifies myserver; the system will return the IP address 165.2.3.5.
Uses of Host table:
The host table has limited role but it is important that your server should have a host table. The host table is used when the DNS is not available for your server. The basic role of the host table is to convert the IP address to host name and vice versa. Hence, it is also used for the reverse DNS (convert IP address to host name). Now a day, most of the systems that have access to the internet rely on DNS for name to address and address to name resolution. But if you have a small network and it does not connect to internet then the host table might be enough for all your needs.
Limitation of Host table:
The host table is a simple text file and you can edit it easily but it is not very easy to search. The file search sequentially for ever host to address and address to host mapping. If the host table size is small then there is no problem but if the size is big then it is not reliable to use host table.
Kailash Aghera
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