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 Sorts of files

Most files are just files, called regular files; they contain normal data, for example text files, executable files or programs, input for or output from a program and so on.

While it is reasonably safe to suppose that everything you encounter on a Linux system is a file, there are some exceptions.

  • Directories: files that are lists of other files.

  • Special files: the mechanism used for input and output. Most special files are in /dev, we will discuss them later.

  • Links: a system to make a file or directory visible in multiple parts of the system's file tree. We will talk about links in detail.

  • (Domain) sockets: a special file type, similar to TCP/IP sockets, providing inter-process networking protected by the file system's access control.

  • Named pipes: act more or less like sockets and form a way for processes to communicate with each other, without using network socket semantics.

The -l option to ls displays the file type, using the first character of each input line:

jaime:~/Documents> ls -l
total 80
-rw-rw-r--   1 jaime   jaime   31744 Feb 21 17:56 intro Linux.doc
-rw-rw-r--   1 jaime   jaime   41472 Feb 21 17:56 Linux.doc
drwxrwxr-x   2 jaime   jaime    4096 Feb 25 11:50 course

This table gives an overview of the characters determining the file type:

Table 3-1. File types in a long list

Symbol Meaning
- Regular file
d Directory
l Link
c Special file
s Socket
p Named pipe
b Block device

In order not to always have to perform a long listing for seeing the file type, a lot of systems by default don't issue just ls, but ls -F, which suffixes file names with one of the characters "/=*|@" to indicate the file type. To make it extra easy on the beginning user, both the -F and --color options are usually combined, see Section We will use ls -F throughout this document for better readability.

As a user, you only need to deal directly with plain files, executable files, directories and links. The special file types are there for making your system do what you demand from it and are dealt with by system administrators and programmers.

Now, before we look at the important files and directories, we need to know more about partitions.

Introducing Linux
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