Linux Basics Unleashed

Linux Basics

Inode

In a file system, a file is represented by an inode, a kind of serial number containing information about the actual data that makes up the file: to whom this file belongs, and where is it located on the hard disk.

Hard link

Associate two or more file names with the same inode. Hard links share the same data blocks on the hard disk, while they continue to behave as independent files.

There is an immediate disadvantage: hard links can't span partitions, because inode numbers are only unique within a given partition.

 Soft link

Soft link or symbolic link (or for short: symlink): a small file that is a pointer to another file. A symbolic link contains the path to the target file instead of a physical location on the hard disk. Since inodes are not used in this system, soft links can span across partitions.

Forking

A new process is created because an existing process makes an exact copy of itself. This child process has the same environment as its parent, only the process ID number is different. This procedure is called forking.

Zombie process

In an exceptional case, a process might finish while the parent does not wait for the completion of this process. Such an unburied process is called a zombie process.

exit status

 exit status is a number returned by the program providing the results of the program's execution.

filesystem

A filesystem is the methods and data structures that an operating system uses to keep track of files on a disk or partition; that is, the way the files are organized on the disk.

Journaling
Journaling is a mechanism whereby a record is kept of transaction which are to be performed, or which have been performed. This allows the filesystem to reconstruct itself fairly easily after damage caused by, for example, improper shutdowns.

Buffer cache

By reading the information from disk only once and then keeping it in memory until no longer needed, one can speed up all but the first read. This is called disk buffering, and the memory used for the purpose is called the buffer cache.