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INTRO(1) Linux User's Manual INTRO(1) 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 im- age viewers and editors, and so on. NOTES Linux is a flavor of UNIX, and as a first approximation all user com- mands 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 com- puter what to do. That is faster and more powerful, but requires find- ing out what the commands are. Below a bare minimum, to get started. Login In order to start working, you probably first have to open a session by giving your username and password. The program login(1) 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. Every- body has their own favorite one. The standard one is called sh. See also ash(1), bash(1), chsh(1), csh(1), dash(1), ksh(1), zsh(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 $ 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, and so on. An assignment PS1="What next, mas- ter? " 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 permis- sions 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" (see stdout(3)), here the terminal screen.) The command cp (from "copy") will copy a file. The command mv (from "move"), on the other hand, 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 giving only 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 alternatively cd and pwd commands and explore cd usage: "cd", "cd .", "cd ..", "cd /" and "cd ~". 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 filesystem found on some disk (or floppy, or CDROM or so) to the big filesystem 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 imme- diate kill. Foreground processes can often be killed by typing Con- trol-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 com- mand "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 introduc- tory 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 ash(1), bash(1), chsh(1), csh(1), dash(1), ksh(1), locate(1), login(1), man(1), xterm(1), zsh(1), wait(2), stdout(3), man-pages(7), stan- dards(7) COLOPHON This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2020-08-13 INTRO(1) INTRO(8) Linux Programmer's Manual INTRO(8) NAME intro - introduction to administration and privileged commands DESCRIPTION Section 8 of the manual describes commands which either can be or are used only by the superuser, like system-administration commands, dae- mons, and hardware-related commands. As with the commands described in 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 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2007-10-23 INTRO(8) INTRO(3) Linux Programmer's Manual INTRO(3) 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 afore- mentioned 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), environ(7), fea- ture_test_macros(7), libc(7), math_error(7), path_resolution(7), pthreads(7), signal(7), standards(7), system_data_types(7) COLOPHON This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2020-11-01 INTRO(3) INTRO(2) Linux Programmer's Manual INTRO(2) 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 func- tion. In many cases, the C library wrapper function does nothing more than: * copying arguments and the unique system call number to the registers where the kernel expects them; * trapping to kernel mode, at which point the kernel does the real work of the system call; * setting errno if the system call returns an error number when the kernel returns the CPU to user mode. However, in a few cases, a wrapper function may do rather more than this, for example, performing some preprocessing of the arguments be- fore trapping to kernel mode, or postprocessing of values returned by the system call. Where this is the case, the manual pages in Section 2 generally try to note the details of both the (usually GNU) C library API interface and the raw system call. Most commonly, the main DE- SCRIPTION will focus on the C library interface, and differences for the system call are covered in the NOTES section. 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 val- ues from a successful call. The details are described in the individ- ual 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 speci- fied 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 fur- ther 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), socket(7), standards(7), system_data_types(7), symlink(7), sysvipc(7), time(7) COLOPHON This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2020-11-01 INTRO(2) INTRO(5) Linux Programmer's Manual INTRO(5) NAME intro - introduction to file formats and filesystems DESCRIPTION Section 5 of the manual describes various file formats, as well as the corresponding C structures, if any. In addition, this section contains a number of pages that document var- ious filesystems. 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 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-03-13 INTRO(5) INTRO(4) Linux Programmer's Manual INTRO(4) 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 mknod(1), mknod(2), standards(7) COLOPHON This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 INTRO(4) INTRO(6) Linux Programmer's Manual INTRO(6) NAME intro - introduction to games DESCRIPTION Section 6 of the manual describes 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 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2007-10-23 INTRO(6) INTRO(7) Linux Programmer's Manual INTRO(7) NAME intro - introduction to overview and miscellany section DESCRIPTION Section 7 of the manual provides overviews on various topics, and de- scribes conventions and protocols, character set standards, the stan- dard filesystem 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 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2007-10-23 INTRO(7)
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