For example: man(1), find(3), updatedb(2)?
What do the numbers in parentheses (Brit. "brackets") mean?
It's the section that the man page for the command is assigned to.
These are split as
General commands
System calls
C library functions
Special files (usually devices, those found in /dev) and drivers
File formats and conventions
Games and screensavers
Miscellanea
System administration commands and daemons
Original descriptions of each section can be seen in the Unix Programmer's Manual (page ii).
In order to access a man page given as "foo(5)", run:
man 5 foo
The section the command is documented in the manual. The list of sections is documented on man's manual. For example:
man 1 man
man 3 find
This is useful for when similar or exactly equal commands exist on different sections
The reason why the section numbers are significant is that many years ago when disk space was more of an issue than it is now the sections could be installed individually.
Many systems only had 1 and 8 installed for instance. These days people tend to look the commands up on google instead.
As #Ian G says, they are the man page sections. Let's take this one step further though:
1. See the man page for the man command with man man, and it shows the 9 sections as follows:
DESCRIPTION
man is the system's manual pager. Each page argument given
to man is normally the name of a program, utility or func‐
tion. The manual page associated with each of these argu‐
ments is then found and displayed. A section, if provided,
will direct man to look only in that section of the manual.
The default action is to search in all of the available sec‐
tions following a pre-defined order ("1 n l 8 3 2 3posix 3pm
3perl 5 4 9 6 7" by default, unless overridden by the SEC‐
TION directive in /etc/manpath.config), and to show only the
first page found, even if page exists in several sections.
The table below shows the section numbers of the manual fol‐
lowed by the types of pages they contain.
1 Executable programs or shell commands
2 System calls (functions provided by the kernel)
3 Library calls (functions within program libraries)
4 Special files (usually found in /dev)
5 File formats and conventions eg /etc/passwd
6 Games
7 Miscellaneous (including macro packages and conven‐
tions), e.g. man(7), groff(7)
8 System administration commands (usually only for root)
9 Kernel routines [Non standard]
A manual page consists of several sections.
2. man <section_num> <cmd>
Let's imagine you are Googling around for Linux commands. You find the OPEN(2) pg online: open(2) — Linux manual page.
To see this in the man pages on your pc, simply type in man 2 open.
For FOPEN(3) use man 3 fopen, etc.
3. man <section_num> intro
To read the intro pages to a section, type in man <section_num> intro, such as man 1 intro, man 2 intro, man 7 intro, etc.
To view all man page intros in succession, one-after-the-other, do man -a intro. The intro page for Section 1 will open. Press q to quit, then press Enter to view the intro for Section 8. Press q to quit, then press Enter to view the intro for Section 3. Continue this process until done. Each time after hitting q, it'll take you back to the main terminal screen but you'll still be in an interactive prompt, and you'll see this line:
--Man-- next: intro(8) [ view (return) | skip (Ctrl-D) | quit (Ctrl-C) ]
Note that the Section order that man -a intro will take you through is:
Section 1
Section 8
Section 3
Section 2
Section 5
Section 4
Section 6
Section 7
This search order is intentional, as the man man page explains:
The default action is to search in all of the available sections follow‐
ing a pre-defined order ("1 n l 8 3 2 3posix 3pm 3perl 5 4 9 6 7" by default, unless overrid‐
den by the SECTION directive in /etc/manpath.config)
Why did they choose this order? I don't know (please answer in the comments if you know), but just realize this order is correct and intentional.
Related:
Google search for "linux what does the number mean in parenthesis after a function?"
SuperUser: What do the parentheses and number after a Unix command or C function mean?
Unix & Linux: What do the numbers in a man page mean?
Note also that on other unixes, the method of specifying the section differs. On solaris, for example, it is:
man -s 1 man
It indicates the section of the man pages the command is found in. The -s switch on the man command can be used to limit a search to certain sections.
When you view a man page, the top left gives the name of the section, e.g.:
User Commands printf(1)
Standard C Library Functions printf(3C)
So if you are trying to look up C functions and don't want to accidentally see a page for a user command that shares the same name, you would do 'man -s 3C ...'
Wikipedia details about Manual Sections:
General commands
System calls
Library functions, covering in particular the C standard library
Special files (usually devices, those found in /dev) and drivers
File formats and conventions
Games and screensavers
Miscellanea
System administration commands and daemons
Related
Why do some linux kernel section names use a single . and others use two
For example .data..page_aligned and .data..init_task vs .data.unlikely and .data.once
Does the number of . have a specific meaning
Thanks
I have read the ld and kernel documentation and not found any information
Section name .data..init_task consists from 3 parts:
Prefix .data.
Delimiter ..
Name of the subsection .init_task.
Since the name of the subsection starts with dot, the section name contains the sequence of two dots.
The section name .data.unlikely consists from 3 parts too, but the name of the subsection - unlikely - is not started with dot.
i have a C program that opens an mp3 and extract the jpg artwork in the same folder. If i execute this program with no root privileges i get a crash. If i execute it with sudo it works normally.
Now, i need another C programs who launch the previous program when it needs a jpg artwork for the selected mp3.
I tried to call popen("./firstProgram test.mp3" , "r") function or system("/(absolute path)/firstProgram test.mp3") function by calling them even with sudo in the command or not and either with relative or absolute paths. But no version seems to work.
How can i launch the first program from the second one with success?
Thanks!
fork and then use execl
char sudo[]="/usr/bin/sudo";
char pbin[]="/usr/local/bin/puppet";
NOTICE("running puppet: %s %s",sudo,pbin);
errno=0;
execl(sudo,sudo,pbin,(char *)NULL);
/* we should never get as far as this */
obviously I recommend reading man execl for further info
Unix (Linux) systems have contained a C Programming Manual in them since possibly forever. Look in Section 2, "System Calls".
This Wikipedia Page explains the Unix Manual "sections"
It is section 2 of the manual you can read about "System Calls"
Try the command: man 2 setuid
This will give you the manual for the setuid() system call which I think is what you want.
That manual page will also list references to other related system calls that may be what you want.
Remember when compiling C programs and using system calls that do low-level hardware access, to use the -O2, or -O3 option to gcc. There is a mention of it in the manual.
Ultimately the setuid() system call makes a running process started by one user change the UID of that running process to be running as some other user. (For example, you may see the Apache running as "apache", even though it was started by root).
setuid(0) lets you be root.
I saw a code snippet using fopen(file_name, "r+e"). What does the e flag mean in fopen? I couldn't find any information from the linux man page.
On a GNU webpage I found that the e means that the "file descriptor will be closed if you use any of the exec… functions".
It's documented in the man page on my system (release 3.54 of the Linux man-pages project).
e (since glibc 2.7)
Open the file with the O_CLOEXEC flag. See open(2) for more information. This flag is ignored for fdopen().
Scroll down; it's under "Glibc notes". This is a non-standard extension.
An online copy of the man page is here.
When I run ls -l /dev on OS X I get an output with the following format (but many more files):
crw-rw-rw- 1 root wheel 4, 126 Jun 11 20:28 ttywe
crw-rw-rw- 1 root wheel 4, 127 Jun 11 20:28 ttywf
As far as I can tell, it is specific to that folder and I can't find anywhere what that 4, means.
I am rewriting ls in C, so I would like to know what it is, and, if possible, how to retrieve that value in C.
From the POSIX specification for ls:
If the file is a character special or block special file, the size of the file may be replaced with implementation-defined information associated with the device in question.
In this particular case, you almost certainly have an implementation printing the major and minor device numbers -- the values which would be passed to mknod to create a file pointing to the same device. However, no implementation is required to provide this information, and your implementation of ls can conform with the standard without it.
If you want to know how to implement this in C, a good place to start is man 2 stat. st_rdev is the field you care about in the struct stat which this call fills out. On Linux, you can extract the major and minor numbers by calling the macros MAJOR(stat_result.st_rdev) and MINOR(stat_result.st_rdev) (assuming you told stat to write to a structure named stat_result).
How can I get current localization (ru-RU, en-US, en-GB, e.t.c.) of Linux through C?
Thank you.
On a POSIX-compliant system, setlocale(LC_CTYPE, NULL); would return the name of the locale currently selected for category LC_CTYPE.
Have a look at the nl_langinfo and the
localeconv man pages.
How to search for subroutines and/or system calls on a Unix system:
query via apropos.
e.g.: apropos locale
look for results which reference man section 2 (system calls) or man section 3. (subroutines).
e.g. on mac:
querylocale(3) - Get locale name for a specified category
setlocale(3) - natural language formatting for C
have a look at the man pages