虚拟文件系统，文件描述符，IO重定向
VFS (Virtual File System)
Inode: 文件的元信息
[root@fobgochod ~]# stat /etc/profile
File: /etc/profile
Size: 2147 Blocks: 8 IO Block: 4096 regular file
Device: fd01h/64769d Inode: 224705 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2021-08-04 23:14:23.726568502 +0800
Modify: 2021-08-04 23:14:17.883351383 +0800
Change: 2021-08-04 23:14:17.884351420 +0800
Birth: -
[root@fobgochod ~]#
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[root@fobgochod ~]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 1.8G 0 1.8G 0% /dev
tmpfs 1.8G 0 1.8G 0% /dev/shm
tmpfs 1.8G 448K 1.8G 1% /run
tmpfs 1.8G 0 1.8G 0% /sys/fs/cgroup
/dev/vda1 40G 2.9G 38G 8% /
tmpfs 363M 0 363M 0% /run/user/0
[root@fobgochod ~]#
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冯·诺依曼(Von Neumann)
计算机的发展史上做出杰出贡献的著名应用数学家
冯·诺依曼计算机结构包含3条重要的设计思想，具体如下：
- 计算机应由
运算器、控制器、存储器、输入设备和输出设备5大部分组成。 - 以二进制的形式表示数据和指令。
- 程序预先存入存储器中，计算机在工作中能够自动地从存储器中取出程序指令并加以执行。
文件类型
- -: 普通文件(可执行文件、图片、文本) REG
- d: 目录
- l: 链接(软链接(windows快捷方式)、硬链接)
- b: 块设备(从一个地方读数据，来回读，如硬盘)
- c: 字符设备(从一个地方读数据，有约束（读不到过去和未来）、如键盘、socket网卡) CHR
- s: socket
- p: pipeline
- [eventpoll]:
硬链接、软链接
硬链接：与普通文件没什么不同，inode 都指向同一个文件在硬盘中的区块
[root@fobgochod ~]# vi test.txt
[root@fobgochod ~]# ln test.txt hard.txt
[root@fobgochod ~]# ll
-rw-r--r-- 2 root root 1 Aug 4 22:51 hard.txt
-rw-r--r-- 2 root root 1 Aug 4 22:51 test.txt
[root@fobgochod ~]#
# 两个文件的Inode:17216191一样
[root@fobgochod ~]# stat test.txt hard.txt
File: test.txt
Size: 1 Blocks: 8 IO Block: 4096 regular file
Device: fd01h/64769d Inode: 17216191 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
File: hard.txt
Size: 1 Blocks: 8 IO Block: 4096 regular file
Device: fd01h/64769d Inode: 17216191 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
[root@fobgochod ~]#
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软链接：保存了其代表的文件的绝对路径，是另外一种文件，在硬盘上有独立的区块，访问时替换自身路径。
[root@fobgochod ~]# ln -s test.txt soft.txt
[root@fobgochod ~]# ll
lrwxrwxrwx 1 root root 8 Aug 4 22:54 soft.txt -> test.txt
-rw-r--r-- 2 root root 1 Aug 4 22:51 test.txt
[root@fobgochod ~]#
# 两个文件的Inode不一样
[root@fobgochod ~]# stat test.txt soft.txt
File: test.txt
Size: 1 Blocks: 8 IO Block: 4096 regular file
Device: fd01h/64769d Inode: 17216191 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
File: soft.txt -> test.txt
Size: 8 Blocks: 0 IO Block: 4096 symbolic link
Device: fd01h/64769d Inode: 16778442 Links: 1
Access: (0777/lrwxrwxrwx) Uid: ( 0/ root) Gid: ( 0/ root)
[root@fobgochod ~]#
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块设备
/dev/null # 黑洞
/dev/zero # 无限大的的空，不占磁盘空间
# if=input file of=output file 1048576=1M
[root@fobgochod ~]# dd if=/dev/zero of=test.img bs=1048576 count=100
104857600 bytes (105 MB, 100 MiB) copied, 0.0397967 s, 2.6 GB/s
[root@fobgochod ~]# ll -h
-rw-r--r-- 1 root root 100M Aug 4 23:00 test.img
[root@fobgochod ~]#
# 挂载mydisk
[root@fobgochod ~]# losetup /dev/loop0 test.img
# 格式化
[root@fobgochod ~]# mke2fs /dev/loop0
# 在mnt下创建image目录
[root@fobgochod ~]# mkdir /mnt/image
[root@fobgochod ~]# cd /mnt/image/
# 挂载
[root@fobgochod image]# mount -t ext2 /dev/loop0 /mnt/image/
[root@fobgochod image]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 1.8G 0 1.8G 0% /dev
/dev/vda1 40G 2.8G 38G 7% /
/dev/loop0 97M 1.6M 91M 2% /mnt/image
[root@fobgochod image]#
[root@fobgochod image]# whereis bash
bash: /usr/bin/bash /usr/share/man/man1/bash.1.gz /usr/share/info/bash.info.gz
[root@fobgochod image]# mkdir bin/
[root@fobgochod image]# cp /usr/bin/bash bin/
[root@fobgochod image]# cd bin
[root@fobgochod bin]# ldd bash
linux-vdso.so.1 (0x00007fff379da000)
libtinfo.so.6 => /lib64/libtinfo.so.6 (0x00007f385d3cf000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f385d1cb000)
libc.so.6 => /lib64/libc.so.6 (0x00007f385ce08000)
/lib64/ld-linux-x86-64.so.2 (0x00007f385d91a000)
[root@fobgochod bin]# cd ..
[root@fobgochod image]# mkdir lib64
[root@fobgochod image]# cp /lib64/{libtinfo.so.6,libdl.so.2,libc.so.6,ld-linux-x86-64.so.2} ./lib64/
[root@fobgochod image]# chroot ./
bash-4.4# echo $$
91229
bash-4.4# echo "hello world" > /abc.txt
bash-4.4# exit
[root@fobgochod image]# ls
abc.txt bin lib64 lost+found
[root@fobgochod image]# cd ..
[root@fobgochod mnt]# umount /mnt/image
[root@fobgochod mnt]# mount -t ext2 /dev/loop0 /mnt/image/
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[root@fobgochod ~]# echo $$
1416
# 0 标准输入 1 标准输出 2 报错输出
[root@fobgochod ~]# lsof -p $$
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
bash 1416 root cwd DIR 253,1 232 16777345 /root
bash 1416 root rtd DIR 253,1 244 128 /
bash 1416 root txt REG 253,1 1150704 33794441 /usr/bin/bash
bash 1416 root mem REG 253,1 3154704 50599498 /usr/lib64/libc-2.28.so
bash 1416 root mem REG 253,1 28968 50599500 /usr/lib64/libdl-2.28.so
bash 1416 root mem REG 253,1 208616 50599346 /usr/lib64/libtinfo.so.6.1
bash 1416 root mem REG 253,1 252280 50599491 /usr/lib64/ld-2.28.so
bash 1416 root mem REG 253,1 26998 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 1416 root 0u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 1u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 2u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 255u CHR 136,0 0t0 3 /dev/pts/0
[root@fobgochod ~]#
[root@fobgochod ~]# exec 8< test.txt
[root@fobgochod ~]# cd /proc/$$/fd
[root@fobgochod fd]# ll
lrwx------ 1 root root 64 Aug 4 22:36 0 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 4 22:36 1 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 4 22:36 2 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 4 22:37 255 -> /dev/pts/0
lr-x------ 1 root root 64 Aug 4 22:36 8 -> /root/test.txt
[root@fobgochod fd]# lsof -op $$
COMMAND PID USER FD TYPE DEVICE OFFSET NODE NAME
bash 1416 root cwd DIR 0,4 27101 /proc/1416/fd
bash 1416 root rtd DIR 253,1 128 /
bash 1416 root txt REG 253,1 33794441 /usr/bin/bash
bash 1416 root mem REG 253,1 50599498 /usr/lib64/libc-2.28.so
bash 1416 root mem REG 253,1 50599500 /usr/lib64/libdl-2.28.so
bash 1416 root mem REG 253,1 50599346 /usr/lib64/libtinfo.so.6.1
bash 1416 root mem REG 253,1 50599491 /usr/lib64/ld-2.28.so
bash 1416 root mem REG 253,1 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 1416 root 0u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 1u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 2u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 8r REG 253,1 0t0 17216191 /root/test.txt
bash 1416 root 255u CHR 136,0 0t0 3 /dev/pts/0
[root@fobgochod fd]#
[root@fobgochod fd]# stat ~/test.txt
File: /root/test.txt
Size: 1 Blocks: 8 IO Block: 4096 regular file
Device: fd01h/64769d Inode: 17216191 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2021-08-04 22:51:42.204868384 +0800
Modify: 2021-08-04 22:51:42.204868384 +0800
Change: 2021-08-04 22:51:47.394060702 +0800
Birth: -
[root@fobgochod fd]#
[root@fobgochod fd]# vi ~/test.txt
aaa
bbb
ccc
[root@fobgochod fd]# read x 0<& 8
[root@fobgochod fd]# echo $x
aaa
[root@fobgochod fd]# lsof -op $$
COMMAND PID USER FD TYPE DEVICE OFFSET NODE NAME
bash 1416 root cwd DIR 0,4 27101 /proc/1416/fd
bash 1416 root rtd DIR 253,1 128 /
bash 1416 root txt REG 253,1 33794441 /usr/bin/bash
bash 1416 root mem REG 253,1 50599498 /usr/lib64/libc-2.28.so
bash 1416 root mem REG 253,1 50599500 /usr/lib64/libdl-2.28.so
bash 1416 root mem REG 253,1 50599346 /usr/lib64/libtinfo.so.6.1
bash 1416 root mem REG 253,1 50599491 /usr/lib64/ld-2.28.so
bash 1416 root mem REG 253,1 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 1416 root 0u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 1u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 2u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 8r REG 253,1 0t4 17216191 /root/test.txt
bash 1416 root 255u CHR 136,0 0t0 3 /dev/pts/0
[root@fobgochod fd]#
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再开一个bash
[root@fobgochod ~]# echo $$
1418
[root@fobgochod ~]# cd /proc/$$/fd
[root@fobgochod fd]# ll
lrwx------ 1 root root 64 Aug 5 00:05 0 -> /dev/pts/2
lrwx------ 1 root root 64 Aug 5 00:05 1 -> /dev/pts/2
lrwx------ 1 root root 64 Aug 5 00:05 2 -> /dev/pts/2
lrwx------ 1 root root 64 Aug 5 00:06 255 -> /dev/pts/2
[root@fobgochod fd]#
[root@fobgochod fd]# exec 9< ~/test.txt
[root@fobgochod fd]# lsof -op $$
COMMAND PID USER FD TYPE DEVICE OFFSET NODE NAME
bash 1418 root cwd DIR 0,4 1556046 /proc/1418/fd
bash 1418 root rtd DIR 253,1 128 /
bash 1418 root txt REG 253,1 33794441 /usr/bin/bash
bash 1418 root mem REG 253,1 50599498 /usr/lib64/libc-2.28.so
bash 1418 root mem REG 253,1 50599500 /usr/lib64/libdl-2.28.so
bash 1418 root mem REG 253,1 50599346 /usr/lib64/libtinfo.so.6.1
bash 1418 root mem REG 253,1 50599491 /usr/lib64/ld-2.28.so
bash 1418 root mem REG 253,1 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 1418 root 0u CHR 136,2 0t0 5 /dev/pts/2
bash 1418 root 1u CHR 136,2 0t0 5 /dev/pts/2
bash 1418 root 2u CHR 136,2 0t0 5 /dev/pts/2
bash 1418 root 9r REG 253,1 0t0 17216191 /root/test.txt
bash 1418 root 255u CHR 136,2 0t0 5 /dev/pts/2
[root@fobgochod fd]#
[root@fobgochod fd]# read x <& 9
[root@fobgochod fd]# echo $x
aaa
[root@fobgochod fd]# read x <& 9
[root@fobgochod fd]# echo $x
bbb
[root@fobgochod fd]# lsof -op $$
COMMAND PID USER FD TYPE DEVICE OFFSET NODE NAME
bash 1418 root cwd DIR 0,4 1556046 /proc/1418/fd
bash 1418 root rtd DIR 253,1 128 /
bash 1418 root txt REG 253,1 33794441 /usr/bin/bash
bash 1418 root mem REG 253,1 50599498 /usr/lib64/libc-2.28.so
bash 1418 root mem REG 253,1 50599500 /usr/lib64/libdl-2.28.so
bash 1418 root mem REG 253,1 50599346 /usr/lib64/libtinfo.so.6.1
bash 1418 root mem REG 253,1 50599491 /usr/lib64/ld-2.28.so
bash 1418 root mem REG 253,1 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 1418 root 0u CHR 136,2 0t0 5 /dev/pts/2
bash 1418 root 1u CHR 136,2 0t0 5 /dev/pts/2
bash 1418 root 2u CHR 136,2 0t0 5 /dev/pts/2
bash 1418 root 9r REG 253,1 0t8 17216191 /root/test.txt
bash 1418 root 255u CHR 136,2 0t0 5 /dev/pts/2
[root@fobgochod fd]#
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socket
[root@fobgochod fd]# exec 10<> /dev/tcp/www.baidu.com/80
[root@fobgochod fd]# ll
lrwx------ 1 root root 64 Aug 4 22:36 0 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 4 22:36 1 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 4 22:36 10 -> 'socket:[2137818]'
lrwx------ 1 root root 64 Aug 4 22:36 2 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 4 22:37 255 -> /dev/pts/0
lr-x------ 1 root root 64 Aug 4 22:36 8 -> /root/test.txt
[root@fobgochod fd]#
[root@fobgochod fd]# lsof -op $$
COMMAND PID USER FD TYPE DEVICE OFFSET NODE NAME
bash 1416 root cwd DIR 0,4 27101 /proc/1416/fd
bash 1416 root rtd DIR 253,1 128 /
bash 1416 root txt REG 253,1 33794441 /usr/bin/bash
bash 1416 root mem REG 253,1 50599498 /usr/lib64/libc-2.28.so
bash 1416 root mem REG 253,1 50599500 /usr/lib64/libdl-2.28.so
bash 1416 root mem REG 253,1 50599346 /usr/lib64/libtinfo.so.6.1
bash 1416 root mem REG 253,1 50599491 /usr/lib64/ld-2.28.so
bash 1416 root mem REG 253,1 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 1416 root 0u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 1u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 2u CHR 136,0 0t0 3 /dev/pts/0
bash 1416 root 8r REG 253,1 0t4 17216191 /root/test.txt
bash 1416 root 10u IPv4 2137818 0t0 TCP fobgochod:50512->112.80.248.76:http (ESTABLISHED)
bash 1416 root 255u CHR 136,0 0t0 3 /dev/pts/0
[root@fobgochod fd]#
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进程
# 任何程序都有
# 0：标准输入
# 1：标准输出
# 2：错误输出
cd /proc
$$: 当前bash的pid
$BASHPID
# 当前进程所有文件描述符
cd /proc/$$/fd
ll
# 文件描述符细节
lsof -op $$
# 重定向：不是命令，是机制
输入：<
输出：>
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重定向
# 基础
# ls标准输出 重定向到 ~/ls.out文件
[root@fobgochod ~]# ls ./ 1> ~/ls.out
# cat标准输入来自 test.txt 标准输入 重定向到 cat.out
[root@fobgochod ~]# cat 0< test.txt 1> cat.out
[root@fobgochod ~]# cat cat.out
aaa
bbb
# read标准输入来自 cat.out
[root@fobgochod ~]# read a 0< cat.out
[root@fobgochod ~]# echo $a
aaa
# 进阶
ls ./ /ooxx 1> ls01.out 2> ls02.out
ls ./ /ooxx 1> ls03.out 2> ls03.out
ls ./ /ooxx 1> ls04.txt 2>& 1
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管道
head test.txt
head -3 test.txt
tail test.txt
tail -3 test.txt
# 文件第八行
head -8 test.txt | tail -1
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父子进程
[root@fobgochod ~]# echo $$
1416
[root@fobgochod ~]# /bin/bash
[root@fobgochod ~]# echo $$
258164
[root@fobgochod ~]# pstree
systemd─┬─chronyd
├─crond
├─lsmd
├─sshd─┬─sshd───sshd─┬─bash───bash───pstree
│ │ ├─bash───top
│ │ └─bash───sleep
│ ├─sshd───sshd───6*[sftp-server]
│ ├─sshd───sshd─┬─bash
│ │ ├─bash───top
│ │ └─bash───sleep
│ └─sshd───sshd───3*[sftp-server]
├─systemd───(sd-pam)
├─systemd-journal
├─systemd-logind
├─systemd-udevd
└─tuned───3*[{tuned}]
[root@fobgochod ~]#
[root@fobgochod ~]# ps -fe | grep 1416
root 1416 1415 0 Aug04 pts/0 00:00:00 -bash
root 258164 1416 0 00:29 pts/0 00:00:00 /bin/bash
root 265453 258164 0 00:31 pts/0 00:00:00 grep --color=auto 1416
[root@fobgochod ~]#
[root@fobgochod ~]# exit
exit
[root@fobgochod ~]# echo $$
1416
[root@fobgochod ~]#
# 变量 export
[root@fobgochod ~]# x=100
[root@fobgochod ~]# echo $x
100
[root@fobgochod ~]# /bin/bash
[root@fobgochod ~]# echo $x
[root@fobgochod ~]# exit
exit
[root@fobgochod ~]# export x
[root@fobgochod ~]# /bin/bash
[root@fobgochod ~]# echo $x
100
[root@fobgochod ~]#
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指令块
{ echo "hello"; echo "world"; }
# 管道两边开启子进程
[root@fobgochod ~]# a=1
[root@fobgochod ~]# echo $a
1
[root@fobgochod ~]# { a=9; echo "hello"; } | cat
hello
[root@fobgochod ~]# echo $a
1
# $$优先级高于管道|
[root@fobgochod ~]# echo $$
1416
[root@fobgochod ~]# echo $$ | cat
1416
[root@fobgochod ~]# echo $BASHPID | cat
277101
[root@fobgochod ~]#
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管道 pipe
[root@fobgochod ~]# echo $$
1416
[root@fobgochod ~]# { echo $BASHPID; read x; } | { cat; echo $BASHPID; read y; }
279249
# 再开一个bash
[root@fobgochod ~]# ps -fe | grep 1416
root 1416 1415 0 Aug04 pts/0 00:00:00 -bash
root 279249 1416 0 00:35 pts/0 00:00:00 -bash
root 279250 1416 0 00:35 pts/0 00:00:00 -bash
root 282370 170282 0 00:36 pts/2 00:00:00 grep --color=auto 1416
[root@fobgochod ~]#
[root@fobgochod fd]# cd /proc/279249/fd
[root@fobgochod fd]# ll
lrwx------ 1 root root 64 Aug 5 00:36 0 -> /dev/pts/0
l-wx------ 1 root root 64 Aug 5 00:36 1 -> 'pipe:[2450910]'
lrwx------ 1 root root 64 Aug 5 00:36 2 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 5 00:36 255 -> /dev/pts/0
[root@fobgochod fd]#
[root@fobgochod fd]# cd /proc/279250/fd
[root@fobgochod fd]# ll
lr-x------ 1 root root 64 Aug 5 00:36 0 -> 'pipe:[2450910]'
lrwx------ 1 root root 64 Aug 5 00:36 1 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 5 00:36 2 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 5 00:36 255 -> /dev/pts/0
[root@fobgochod fd]#
[root@fobgochod fd]# lsof -op 279249
[root@fobgochod fd]# lsof -op 279249
COMMAND PID USER FD TYPE DEVICE OFFSET NODE NAME
bash 279249 root cwd DIR 253,1 16777345 /root
bash 279249 root rtd DIR 253,1 128 /
bash 279249 root txt REG 253,1 33794441 /usr/bin/bash
bash 279249 root mem REG 253,1 50599498 /usr/lib64/libc-2.28.so
bash 279249 root mem REG 253,1 50599500 /usr/lib64/libdl-2.28.so
bash 279249 root mem REG 253,1 50599346 /usr/lib64/libtinfo.so.6.1
bash 279249 root mem REG 253,1 50599491 /usr/lib64/ld-2.28.so
bash 279249 root mem REG 253,1 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 279249 root 0u CHR 136,0 0t0 3 /dev/pts/0
bash 279249 root 1w FIFO 0,13 0t0 2450910 pipe
bash 279249 root 2u CHR 136,0 0t0 3 /dev/pts/0
bash 279249 root 255u CHR 136,0 0t0 3 /dev/pts/0
[root@fobgochod fd]#
[root@fobgochod fd]# lsof -op 279250
COMMAND PID USER FD TYPE DEVICE OFFSET NODE NAME
bash 279250 root cwd DIR 253,1 16777345 /root
bash 279250 root rtd DIR 253,1 128 /
bash 279250 root txt REG 253,1 33794441 /usr/bin/bash
bash 279250 root mem REG 253,1 50599498 /usr/lib64/libc-2.28.so
bash 279250 root mem REG 253,1 50599500 /usr/lib64/libdl-2.28.so
bash 279250 root mem REG 253,1 50599346 /usr/lib64/libtinfo.so.6.1
bash 279250 root mem REG 253,1 50599491 /usr/lib64/ld-2.28.so
bash 279250 root mem REG 253,1 33794440 /usr/lib64/gconv/gconv-modules.cache
bash 279250 root 0r FIFO 0,13 0t0 2450910 pipe
bash 279250 root 1u CHR 136,0 0t0 3 /dev/pts/0
bash 279250 root 2u CHR 136,0 0t0 3 /dev/pts/0
bash 279250 root 255u CHR 136,0 0t0 3 /dev/pts/0
[root@fobgochod fd]#
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PageCache
- 又称pcache，其中文名称为页高速缓冲存储器，简称页高缓
- page cache的大小为一页，通常为4K
- 内核会在以下三种情况下将dirty page 写回磁盘:
- 用户进程调用sync() 和 fsync()系统调用
- 空闲内存低于特定的阈值(threshold)
- Dirty数据在内存中驻留的时间超过一个特定的阈值
缓存
int 0x80 int cpu指令 0x80：128 1000 0000 值、寄存器
中断描述符表 0 1 2 128 call back（保护现场、切换用户态、内核态） 255
协处理器 DMA
- DMA，全称Direct Memory Access，即直接存储器访问。
rm -rf *out*
javac OSFileIO.java
strace -ff -o out java OSFileIO $1
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