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《Linux/Unix系统编程手册》读书笔记7 （/proc文件的简介和运用）

时间：2022-04-03 08:57

《Linux/Unix系统编程手册》读书笔记目录

第11章

这章主要讲了关于Linux和UNIX的系统资源的限制。

关于限制都存在一个最小值，这些最小值为<limits.h>文件中的常量。

通过cat 命令查看：

lancelot@debian:~/Code/tlpi$ cat /usr/include/limits.h 
/* Copyright (C) 1991, 1992, 1996, 1997, 1998, 1999, 2000, 2005
   Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

/*
 *    ISO C99 Standard: 7.10/5.2.4.2.1 Sizes of integer types    <limits.h>
 */

#ifndef _LIBC_LIMITS_H_
#define _LIBC_LIMITS_H_    1

#include <features.h>


/* Maximum length of any multibyte character in any locale.
   We define this value here since the gcc header does not define
   the correct value.  */
#define MB_LEN_MAX    16


/* If we are not using GNU CC we have to define all the symbols ourself.
   Otherwise use gcc‘s definitions (see below).  */
#if !defined __GNUC__ || __GNUC__ < 2

/* We only protect from multiple inclusion here, because all the other
   #include‘s protect themselves, and in GCC 2 we may #include_next through
   multiple copies of this file before we get to GCC‘s.  */
# ifndef _LIMITS_H
#  define _LIMITS_H    1

#include <bits/wordsize.h>

/* We don‘t have #include_next.
   Define ANSI <limits.h> for standard 32-bit words.  */

/* These assume 8-bit `char‘s, 16-bit `short int‘s,
   and 32-bit `int‘s and `long int‘s.  */

/* Number of bits in a `char‘.    */
#  define CHAR_BIT    8

/* Minimum and maximum values a `signed char‘ can hold.  */
#  define SCHAR_MIN    (-128)
#  define SCHAR_MAX    127

/* Maximum value an `unsigned char‘ can hold.  (Minimum is 0.)  */
#  define UCHAR_MAX    255

/* Minimum and maximum values a `char‘ can hold.  */
#  ifdef __CHAR_UNSIGNED__
#   define CHAR_MIN    0
#   define CHAR_MAX    UCHAR_MAX
#  else
#   define CHAR_MIN    SCHAR_MIN
#   define CHAR_MAX    SCHAR_MAX
#  endif

/* Minimum and maximum values a `signed short int‘ can hold.  */
#  define SHRT_MIN    (-32768)
#  define SHRT_MAX    32767

/* Maximum value an `unsigned short int‘ can hold.  (Minimum is 0.)  */
#  define USHRT_MAX    65535

/* Minimum and maximum values a `signed int‘ can hold.  */
#  define INT_MIN    (-INT_MAX - 1)
#  define INT_MAX    2147483647

/* Maximum value an `unsigned int‘ can hold.  (Minimum is 0.)  */
#  define UINT_MAX    4294967295U

/* Minimum and maximum values a `signed long int‘ can hold.  */
#  if __WORDSIZE == 64
#   define LONG_MAX    9223372036854775807L
#  else
#   define LONG_MAX    2147483647L
#  endif
#  define LONG_MIN    (-LONG_MAX - 1L)

/* Maximum value an `unsigned long int‘ can hold.  (Minimum is 0.)  */
#  if __WORDSIZE == 64
#   define ULONG_MAX    18446744073709551615UL
#  else
#   define ULONG_MAX    4294967295UL
#  endif

#  ifdef __USE_ISOC99

/* Minimum and maximum values a `signed long long int‘ can hold.  */
#   define LLONG_MAX    9223372036854775807LL
#   define LLONG_MIN    (-LLONG_MAX - 1LL)

/* Maximum value an `unsigned long long int‘ can hold.  (Minimum is 0.)  */
#   define ULLONG_MAX    18446744073709551615ULL

#  endif /* ISO C99 */

# endif    /* limits.h  */
#endif    /* GCC 2.  */

#endif    /* !_LIBC_LIMITS_H_ */

 /* Get the compiler‘s limits.h, which defines almost all the ISO constants.

    We put this #include_next outside the double inclusion check because
    it should be possible to include this file more than once and still get
    the definitions from gcc‘s header.  */
#if defined __GNUC__ && !defined _GCC_LIMITS_H_
/* `_GCC_LIMITS_H_‘ is what GCC‘s file defines.  */
# include_next <limits.h>
#endif

/* The <limits.h> files in some gcc versions don‘t define LLONG_MIN,
   LLONG_MAX, and ULLONG_MAX.  Instead only the values gcc defined for
   ages are available.  */
#if defined __USE_ISOC99 && defined __GNUC__
# ifndef LLONG_MIN
#  define LLONG_MIN    (-LLONG_MAX-1)
# endif
# ifndef LLONG_MAX
#  define LLONG_MAX    __LONG_LONG_MAX__
# endif
# ifndef ULLONG_MAX
#  define ULLONG_MAX    (LLONG_MAX * 2ULL + 1)
# endif
#endif

#ifdef    __USE_POSIX
/* POSIX adds things to <limits.h>.  */
# include <bits/posix1_lim.h>
#endif

#ifdef    __USE_POSIX2
# include <bits/posix2_lim.h>
#endif

#ifdef    __USE_XOPEN
# include <bits/xopen_lim.h>
#endif

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我们还可以通过在shell用getconf获取限制：

PS：OPEN_MAX为进程同时最多可以打开的文件描述符的数量。

lancelot@debian:~/Code/tlpi$ getconf OPEN_MAX
1024

第12章

这章主要将了系统和进程信息

/proc虚拟文件系统：维基

首先我们来看看/proc有些什么

lancelot@debian:~/Code/tlpi$ sudo cat /proc/1/maps 
00400000-00409000 r-xp 00000000 08:08 9306173                            /sbin/init
00608000-00609000 rw-p 00008000 08:08 9306173                            /sbin/init
01e15000-01e36000 rw-p 00000000 00:00 0                                  [heap]
7f5109159000-7f510915b000 r-xp 00000000 08:08 1838382                    /lib/x86_64-linux-gnu/libdl-2.13.so
7f510915b000-7f510935b000 ---p 00002000 08:08 1838382                    /lib/x86_64-linux-gnu/libdl-2.13.so
7f510935b000-7f510935c000 r--p 00002000 08:08 1838382                    /lib/x86_64-linux-gnu/libdl-2.13.so
7f510935c000-7f510935d000 rw-p 00003000 08:08 1838382                    /lib/x86_64-linux-gnu/libdl-2.13.so
7f510935d000-7f51094df000 r-xp 00000000 08:08 1835094                    /lib/x86_64-linux-gnu/libc-2.13.so
7f51094df000-7f51096de000 ---p 00182000 08:08 1835094                    /lib/x86_64-linux-gnu/libc-2.13.so
7f51096de000-7f51096e2000 r--p 00181000 08:08 1835094                    /lib/x86_64-linux-gnu/libc-2.13.so
7f51096e2000-7f51096e3000 rw-p 00185000 08:08 1835094                    /lib/x86_64-linux-gnu/libc-2.13.so
7f51096e3000-7f51096e8000 rw-p 00000000 00:00 0 
7f51096e8000-7f5109706000 r-xp 00000000 08:08 1835054                    /lib/x86_64-linux-gnu/libselinux.so.1
7f5109706000-7f5109905000 ---p 0001e000 08:08 1835054                    /lib/x86_64-linux-gnu/libselinux.so.1
7f5109905000-7f5109906000 r--p 0001d000 08:08 1835054                    /lib/x86_64-linux-gnu/libselinux.so.1
7f5109906000-7f5109907000 rw-p 0001e000 08:08 1835054                    /lib/x86_64-linux-gnu/libselinux.so.1
7f5109907000-7f5109908000 rw-p 00000000 00:00 0 
7f5109908000-7f5109947000 r-xp 00000000 08:08 1835059                    /lib/x86_64-linux-gnu/libsepol.so.1
7f5109947000-7f5109b46000 ---p 0003f000 08:08 1835059                    /lib/x86_64-linux-gnu/libsepol.so.1
7f5109b46000-7f5109b47000 r--p 0003e000 08:08 1835059                    /lib/x86_64-linux-gnu/libsepol.so.1
7f5109b47000-7f5109b48000 rw-p 0003f000 08:08 1835059                    /lib/x86_64-linux-gnu/libsepol.so.1
7f5109b48000-7f5109b68000 r-xp 00000000 08:08 1838390                    /lib/x86_64-linux-gnu/ld-2.13.so
7f5109d4a000-7f5109d4e000 rw-p 00000000 00:00 0 
7f5109d65000-7f5109d67000 rw-p 00000000 00:00 0 
7f5109d67000-7f5109d68000 r--p 0001f000 08:08 1838390                    /lib/x86_64-linux-gnu/ld-2.13.so
7f5109d68000-7f5109d69000 rw-p 00020000 08:08 1838390                    /lib/x86_64-linux-gnu/ld-2.13.so
7f5109d69000-7f5109d6a000 rw-p 00000000 00:00 0 
7fffc8fe9000-7fffc900a000 rw-p 00000000 00:00 0                          [stack]
7fffc9191000-7fffc9192000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]

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mem为进程虚拟内存

mounts为进程的安装点

lancelot@debian:~/Code/tlpi$ sudo cat /proc/1/mounts
rootfs / rootfs rw 0 0
sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
udev /dev devtmpfs rw,relatime,size=10240k,nr_inodes=958260,mode=755 0 0
devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /run tmpfs rw,nosuid,noexec,relatime,size=767824k,mode=755 0 0
/dev/disk/by-uuid/c2a06636-4fcf-4701-8f46-6415015254a0 / ext4 rw,relatime,errors=remount-ro,user_xattr,barrier=1,data=ordered 0 0
tmpfs /run/lock tmpfs rw,nosuid,nodev,noexec,relatime,size=5120k 0 0
tmpfs /run/shm tmpfs rw,nosuid,nodev,noexec,relatime,size=1535640k 0 0
/dev/sda7 /boot ext4 rw,relatime,user_xattr,barrier=1,stripe=4,data=ordered 0 0
/dev/sda5 /home ext4 rw,relatime,user_xattr,barrier=1,data=ordered 0 0
/dev/sda6 /opt ext4 rw,relatime,user_xattr,barrier=1,data=ordered 0 0
rpc_pipefs /var/lib/nfs/rpc_pipefs rpc_pipefs rw,relatime 0 0
binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc rw,nosuid,nodev,noexec,relatime 0 0

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root为指向根目录的符号链接

status记录着进程的ID、内存使用情况、信号等信息。

lancelot@debian:~/Code/tlpi$ sudo cat /proc/1/status 
Name:    init
State:    S (sleeping)
Tgid:    1
Pid:    1
PPid:    0
TracerPid:    0
Uid:    0    0    0    0
Gid:    0    0    0    0
FDSize:    64
Groups:    
VmPeak:       10652 kB
VmSize:       10648 kB
VmLck:           0 kB
VmPin:           0 kB
VmHWM:         788 kB
VmRSS:         788 kB
VmData:         188 kB
VmStk:         136 kB
VmExe:          36 kB
VmLib:        2052 kB
VmPTE:          44 kB
VmSwap:           0 kB
Threads:    1
SigQ:    0/59891
SigPnd:    0000000000000000
ShdPnd:    0000000000000000
SigBlk:    0000000000000000
SigIgn:    fffffffe57f0d8fc
SigCgt:    00000000280b2603
CapInh:    0000000000000000
CapPrm:    ffffffffffffffff
CapEff:    ffffffffffffffff
CapBnd:    ffffffffffffffff
Cpus_allowed:    f
Cpus_allowed_list:    0-3
Mems_allowed:    00000000,00000001
Mems_allowed_list:    0
voluntary_ctxt_switches:    7947
nonvoluntary_ctxt_switches:    33

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task下存放着该进程的每个线程的子目录（记录线程的信息）

lancelot@debian:~/Code/tlpi$ sudo ls -l /proc/1/task
总用量 0
dr-xr-xr-x 6 root root 0  4月 28 23:07 1

子目录的信息：

lancelot@debian:~/Code/tlpi$ sudo ls -l /proc/1/task/1
总用量 0
dr-xr-xr-x 2 root root 0  4月 28 23:08 attr
-r-------- 1 root root 0  4月 28 23:08 auxv
-r--r--r-- 1 root root 0  4月 28 23:08 cgroup
--w------- 1 root root 0  4月 28 23:08 clear_refs
-r--r--r-- 1 root root 0  4月 28 23:08 cmdline
-rw-r--r-- 1 root root 0  4月 28 23:08 comm
-r--r--r-- 1 root root 0  4月 28 23:08 cpuset
lrwxrwxrwx 1 root root 0  4月 28 23:08 cwd -> /
-r-------- 1 root root 0  4月 28 23:08 environ
lrwxrwxrwx 1 root root 0  4月 28 23:08 exe -> /sbin/init
dr-x------ 2 root root 0  4月 28 23:08 fd
dr-x------ 2 root root 0  4月 28 23:08 fdinfo
-r-------- 1 root root 0  4月 28 23:08 io
-r--r--r-- 1 root root 0  4月 28 23:08 limits
-rw-r--r-- 1 root root 0  4月 28 23:08 loginuid
-r--r--r-- 1 root root 0  4月 28 23:08 maps
-rw------- 1 root root 0  4月 28 23:08 mem
-r--r--r-- 1 root root 0  4月 28 23:08 mountinfo
-r--r--r-- 1 root root 0  4月 28 23:08 mounts
dr-x--x--x 2 root root 0  4月 28 23:08 ns
-r--r--r-- 1 root root 0  4月 28 23:08 numa_maps
-rw-r--r-- 1 root root 0  4月 28 23:08 oom_adj
-r--r--r-- 1 root root 0  4月 28 23:08 oom_score
-rw-r--r-- 1 root root 0  4月 28 23:08 oom_score_adj
-r--r--r-- 1 root root 0  4月 28 23:08 pagemap
-r--r--r-- 1 root root 0  4月 28 23:08 personality
lrwxrwxrwx 1 root root 0  4月 28 23:08 root -> /
-rw-r--r-- 1 root root 0  4月 28 23:08 sched
-r--r--r-- 1 root root 0  4月 28 23:08 sessionid
-r--r--r-- 1 root root 0  4月 28 23:08 smaps
-r--r--r-- 1 root root 0  4月 28 23:08 stack
-r--r--r-- 1 root root 0  4月 28 23:08 stat
-r--r--r-- 1 root root 0  4月 28 23:08 statm
-r--r--r-- 1 root root 0  4月 28 23:08 status
-r--r--r-- 1 root root 0  4月 28 23:08 syscall
-r--r--r-- 1 root root 0  4月 28 23:08 wchan

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通过访问/proc文件可以获取很多有用的信息。

练习：

12-1.编写一个程序，以用户名作为命令行参数，列表显示该用户下所有正在运行的进程ID和命令名。通过分析系统中/proc/PID/status文件的Name和UID各行信息，可以思想此功能。