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intro

Introduction to user commands


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1. intro.1.man

Manpage of INTRO

INTRO

Section: Linux User's Manual (1)
Updated: 2007-11-15
Index Return to Main Contents
 

NAME

intro - Introduction to user commands  

DESCRIPTION

Section 1 of the manual describes user commands and tools, for example, file manipulation tools, shells, compilers, web browsers, file and image viewers and editors, and so on.

All commands yield a status value on termination. This value can be tested (e.g., in most shells the variable $? contains the status of the last executed command) to see whether the command completed successfully. A zero exit status is conventionally used to indicate success, and a nonzero status means that the command was unsuccessful. (Details of the exit status can be found in wait(2).) A nonzero exit status can be in the range 1 to 255, and some commands use different nonzero status values to indicate the reason why the command failed.  

NOTES

Linux is a flavor of UNIX, and as a first approximation all user commands under UNIX work precisely the same under Linux (and FreeBSD and lots of other UNIX-like systems).

Under Linux there are GUIs (graphical user interfaces), where you can point and click and drag, and hopefully get work done without first reading lots of documentation. The traditional UNIX environment is a CLI (command line interface), where you type commands to tell the computer what to do. That is faster and more powerful, but requires finding out what the commands are. Below a bare minimum, to get started.  

Login

In order to start working, you probably first have to login, that is, give your username and password. See also login(1). The program login now starts a shell (command interpreter) for you. In case of a graphical login, you get a screen with menus or icons and a mouse click will start a shell in a window. See also xterm(1).  

The shell

One types commands to the shell, the command interpreter. It is not built-in, but is just a program and you can change your shell. Everybody has her own favorite one. The standard one is called sh. See also ash(1), bash(1), csh(1), zsh(1), chsh(1).

A session might go like

knuth login: aeb
Password: ********
% date
Tue Aug  6 23:50:44 CEST 2002
% cal
     August 2002
Su Mo Tu We Th Fr Sa
             1  2  3
 4  5  6  7  8  9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31

% ls
bin  tel
% ls -l
total 2
drwxrwxr-x   2 aeb       1024 Aug  6 23:51 bin
-rw-rw-r--   1 aeb         37 Aug  6 23:52 tel
% cat tel
maja    0501-1136285
peter   0136-7399214
% cp tel tel2
% ls -l
total 3
drwxr-xr-x   2 aeb       1024 Aug  6 23:51 bin
-rw-r--r--   1 aeb         37 Aug  6 23:52 tel
-rw-r--r--   1 aeb         37 Aug  6 23:53 tel2
% mv tel tel1
% ls -l
total 3
drwxr-xr-x   2 aeb       1024 Aug  6 23:51 bin
-rw-r--r--   1 aeb         37 Aug  6 23:52 tel1
-rw-r--r--   1 aeb         37 Aug  6 23:53 tel2
% diff tel1 tel2
% rm tel1
% grep maja tel2
maja    0501-1136285
% 
and here typing Control-D ended the session. The % here was the command prompt --- it is the shell's way of indicating that it is ready for the next command. The prompt can be customized in lots of ways, and one might include stuff like username, machine name, current directory, time, etc. An assignment PS1="What next, master? " would change the prompt as indicated.

We see that there are commands date (that gives date and time), and cal (that gives a calendar).

The command ls lists the contents of the current directory --- it tells you what files you have. With a -l option it gives a long listing, that includes the owner and size and date of the file, and the permissions people have for reading and/or changing the file. For example, the file "tel" here is 37 bytes long, owned by aeb and the owner can read and write it, others can only read it. Owner and permissions can be changed by the commands chown and chmod.

The command cat will show the contents of a file. (The name is from "concatenate and print": all files given as parameters are concatenated and sent to "standard output", here the terminal screen.)

The command cp (from "copy") will copy a file. On the other hand, the command mv (from "move") only renames it.

The command diff lists the differences between two files. Here there was no output because there were no differences.

The command rm (from "remove") deletes the file, and be careful! it is gone. No wastepaper basket or anything. Deleted means lost.

The command grep (from "g/re/p") finds occurrences of a string in one or more files. Here it finds Maja's telephone number.  

Pathnames and the current directory

Files live in a large tree, the file hierarchy. Each has a pathname describing the path from the root of the tree (which is called /) to the file. For example, such a full pathname might be /home/aeb/tel. Always using full pathnames would be inconvenient, and the name of a file in the current directory may be abbreviated by only giving the last component. That is why "/home/aeb/tel" can be abbreviated to "tel" when the current directory is "/home/aeb".

The command pwd prints the current directory.

The command cd changes the current directory. Try "cd /" and "pwd" and "cd" and "pwd".  

Directories

The command mkdir makes a new directory.

The command rmdir removes a directory if it is empty, and complains otherwise.

The command find (with a rather baroque syntax) will find files with given name or other properties. For example, "find . -name tel" would find the file "tel" starting in the present directory (which is called "."). And "find / -name tel" would do the same, but starting at the root of the tree. Large searches on a multi-GB disk will be time-consuming, and it may be better to use locate(1).  

Disks and Filesystems

The command mount will attach the file system found on some disk (or floppy, or CDROM or so) to the big file system hierarchy. And umount detaches it again. The command df will tell you how much of your disk is still free.  

Processes

On a UNIX system many user and system processes run simultaneously. The one you are talking to runs in the foreground, the others in the background. The command ps will show you which processes are active and what numbers these processes have. The command kill allows you to get rid of them. Without option this is a friendly request: please go away. And "kill -9" followed by the number of the process is an immediate kill. Foreground processes can often be killed by typing Control-C.  

Getting information

There are thousands of commands, each with many options. Traditionally commands are documented on man pages, (like this one), so that the command "man kill" will document the use of the command "kill" (and "man man" document the command "man"). The program man sends the text through some pager, usually less. Hit the space bar to get the next page, hit q to quit.

In documentation it is customary to refer to man pages by giving the name and section number, as in man(1). Man pages are terse, and allow you to find quickly some forgotten detail. For newcomers an introductory text with more examples and explanations is useful.

A lot of GNU/FSF software is provided with info files. Type "info info" for an introduction on the use of the program "info".

Special topics are often treated in HOWTOs. Look in /usr/share/doc/howto/en and use a browser if you find HTML files there.  

SEE ALSO

standards(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
NOTES
Login
The shell
Pathnames and the current directory
Directories
Disks and Filesystems
Processes
Getting information
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

2. intro.2.man

Manpage of INTRO

INTRO

Section: Linux Programmer's Manual (2)
Updated: 2010-11-11
Index Return to Main Contents
 

NAME

intro - Introduction to system calls  

DESCRIPTION

Section 2 of the manual describes the Linux system calls. A system call is an entry point into the Linux kernel. Usually, system calls are not invoked directly: instead, most system calls have corresponding C library wrapper functions which perform the steps required (e.g., trapping to kernel mode) in order to invoke the system call. Thus, making a system call looks the same as invoking a normal library function.

For a list of the Linux system calls, see syscalls(2).  

RETURN VALUE

On error, most system calls return a negative error number (i.e., the negated value of one of the constants described in errno(3)). The C library wrapper hides this detail from the caller: when a system call returns a negative value, the wrapper copies the absolute value into the errno variable, and returns -1 as the return value of the wrapper.

The value returned by a successful system call depends on the call. Many system calls return 0 on success, but some can return nonzero values from a successful call. The details are described in the individual manual pages.

In some cases, the programmer must define a feature test macro in order to obtain the declaration of a system call from the header file specified in the man page SYNOPSIS section. (Where required, these feature test macros must be defined before including any header files.) In such cases, the required macro is described in the man page. For further information on feature test macros, see feature_test_macros(7).  

CONFORMING TO

Certain terms and abbreviations are used to indicate UNIX variants and standards to which calls in this section conform. See standards(7).  

NOTES

 

Calling Directly

In most cases, it is unnecessary to invoke a system call directly, but there are times when the Standard C library does not implement a nice wrapper function for you. In this case, the programmer must manually invoke the system call using syscall(2). Historically, this was also possible using one of the _syscall macros described in _syscall(2).  

Authors and Copyright Conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!  

SEE ALSO

_syscall(2), syscall(2), syscalls(2), errno(3), intro(3), capabilities(7), credentials(7), feature_test_macros(7), mq_overview(7), path_resolution(7), pipe(7), pty(7), sem_overview(7), shm_overview(7), signal(7), svipc(7), standards(7), socket(7), symlink(7), time(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
RETURN VALUE
CONFORMING TO
NOTES
Calling Directly
Authors and Copyright Conditions
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

3. intro.3.man

Manpage of INTRO

INTRO

Section: Linux Programmer's Manual (3)
Updated: 2010-11-11
Index Return to Main Contents
 

NAME

intro - Introduction to library functions  

DESCRIPTION

Section 3 of the manual describes all library functions excluding the library functions (system call wrappers) described in section 2, which implement system calls.

Many of the functions described in the section are part of the Standard C Library (libc). Some functions are part of other libraries (e.g., the math library, libm, or the real-time library, librt) in which case the manual page will indicate the linker option needed to link against the required library (e.g., -lm and -lrt, respectively, for the aforementioned libraries).

In some cases, the programmer must define a feature test macro in order to obtain the declaration of a function from the header file specified in the man page SYNOPSIS section. (Where required, these feature test macros must be defined before including any header files.) In such cases, the required macro is described in the man page. For further information on feature test macros, see feature_test_macros(7).  

CONFORMING TO

Certain terms and abbreviations are used to indicate UNIX variants and standards to which calls in this section conform. See standards(7).  

NOTES

 

Authors and Copyright Conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!  

SEE ALSO

intro(2), errno(3), capabilities(7), credentials(7), feature_test_macros(7), libc(7), math_error(7), environ(7), path_resolution(7), pthreads(7), signal(7), standards(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
CONFORMING TO
NOTES
Authors and Copyright Conditions
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

4. intro.4.man

Manpage of INTRO

INTRO

Section: Linux Programmer's Manual (4)
Updated: 2007-10-23
Index Return to Main Contents
 

NAME

intro - Introduction to special files  

DESCRIPTION

Section 4 of the manual describes special files (devices).  

FILES

/dev/* --- device files  

NOTES

 

Authors and Copyright Conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!  

SEE ALSO

standards(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
FILES
NOTES
Authors and Copyright Conditions
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

5. intro.5.man

Manpage of INTRO

INTRO

Section: Linux Programmer's Manual (5)
Updated: 2007-10-23
Index Return to Main Contents
 

NAME

intro - Introduction to file formats  

DESCRIPTION

Section 5 of the manual describes various file formats and protocols, and the corresponding C structures, if any.  

NOTES

 

Authors and Copyright Conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!  

SEE ALSO

standards(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
NOTES
Authors and Copyright Conditions
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

6. intro.6.man

Manpage of INTRO

INTRO

Section: Linux Programmer's Manual (6)
Updated: 2007-10-23
Index Return to Main Contents
 

NAME

intro - Introduction to games  

DESCRIPTION

Section 6 of the manual describes all the games and funny little programs available on the system.  

NOTES

 

Authors and Copyright Conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
NOTES
Authors and Copyright Conditions
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

7. intro.7.man

Manpage of INTRO

INTRO

Section: Linux Programmer's Manual (7)
Updated: 2007-10-23
Index Return to Main Contents
 

NAME

intro - Introduction to overview, conventions, and miscellany section  

DESCRIPTION

Section 7 of the manual provides overviews on various topics, and describes conventions and protocols, character set standards, the standard file system layout, and miscellaneous other things.  

NOTES

 

Authors and Copyright Conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!  

SEE ALSO

standards(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
NOTES
Authors and Copyright Conditions
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

8. intro.8.man

Manpage of INTRO

INTRO

Section: Linux Programmer's Manual (8)
Updated: 2007-10-23
Index Return to Main Contents
 

NAME

intro - Introduction to administration and privileged commands  

DESCRIPTION

Section 8 of the manual describes commands which either can be or are only used by the superuser, like system-administration commands, daemons, and hardware-related commands.

As with the commands in described section 1, the commands described in this section terminate with an exit status that indicates whether the command succeeded or failed. See intro(1) for more information.  

NOTES

 

Authors and Copyright Conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
NOTES
Authors and Copyright Conditions
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:31:14 GMT, October 23, 2013

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