Linux笔记--man指令（福利）

介绍

Linux提供了一个帮助手册，可以供使用者进行查询。

格式

man 代号数据

1 使用者在shell中可以操作的指令或可执行档
2 系統核心可呼叫的函数与工具等
3 一些常用的函数(function)与函数库(library)，大部分是C的函数库(libc)
4 装置档案的说明，通常在/dev下的档案
5 设定档或者是某些档案的格式
6 游戏(games)
7 惯例与协定等，例如Linux档案系统、网络协定、ASCII code等等的說明
8 系統管理員可用的管理指令
9 跟kernel有关的文件

举例

终端输入 man 2 getpid

即可显示 getpid函数的相关信息

GETPID(2)                                  Linux Programmer's Manual                                  GETPID(2)NAMEgetpid, getppid - get process identificationSYNOPSIS#include <sys/types.h>#include <unistd.h>pid_t getpid(void);pid_t getppid(void);DESCRIPTIONgetpid() returns the process ID (PID) of the calling process.  (This is often used by routines that gen‐erate unique temporary filenames.)getppid() returns the process ID of the parent of the calling process.  This will be either  the  ID  ofthe  process  that created this process using fork(), or, if that process has already terminated, the IDof the process to which this process has been reparented (either init(1) or a  "subreaper"  process  de‐fined via the prctl(2) PR_SET_CHILD_SUBREAPER operation).ERRORSThese functions are always successful.CONFORMING TOPOSIX.1-2001, POSIX.1-2008, 4.3BSD, SVr4.NOTESIf the caller's parent is in a different PID namespace (see pid_namespaces(7)), getppid() returns 0.From a kernel perspective, the PID (which is shared by all of the threads in a multithreaded process) issometimes also known as the thread group ID (TGID).  This contrasts with the  kernel  thread  ID  (TID),which  is  unique  for  each  thread.   For  further  details,  see  gettid(2) and the discussion of theCLONE_THREAD flag in clone(2).C library/kernel differencesFrom glibc version 2.3.4 up to and including version 2.24,  the  glibc  wrapper  function  for  getpid()cached PIDs, with the goal of avoiding additional system calls when a process calls getpid() repeatedly.Normally this caching was invisible, but its correct operation relied on support in  the  wrapper  func‐tions  for fork(2), vfork(2), and clone(2): if an application bypassed the glibc wrappers for these sys‐tem calls by using syscall(2), then a call to getpid() in the child would return the wrong value (to  beprecise:  it  would return the PID of the parent process).  In addition, there were cases where getpid()could return the wrong value even when invoking clone(2) via the glibc wrapper function.  (For a discus‐sion  of one such case, see BUGS in clone(2).)  Furthermore, the complexity of the caching code had beenthe source of a few bugs within glibc over the years.Because of the aforementioned problems, since glibc version 2.25, the PID cache  is  removed:  calls  togetpid() always invoke the actual system call, rather than returning a cached value.SEE ALSOclone(2),  fork(2),  gettid(2), kill(2), exec(3), mkstemp(3), tempnam(3), tmpfile(3), tmpnam(3), creden‐tials(7), pid_namespaces(7)COLOPHONThis page is part of release 4.16 of the Linux man-pages project.  A description of the project,  infor‐mation   about   reporting   bugs,   and   the   latest   version   of   this  page,  can  be  found  athttps://www.kernel.org/doc/man-pages/.Linux                                              2017-11-26

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Linux笔记--man指令（福利）

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