2017年10月26日笔记

旧城等待， 2022-06-06 01:10 217阅读 0赞

\[root@localhost pts\]\#  ***who am i***  
root     pts/3        2017-10-26 08:47 (192.168.30.1)  
\[root@localhost pts\]\# ***who***  
root     tty1         2017-10-24 19:32  
root     pts/3        2017-10-26 08:47 (192.168.30.1)  
root     pts/4        2017-10-26 08:49 (192.168.30.1)  
\[root@localhost pts\]\# ***w***  
 09:24:55 up 16:43,  3 users,  load average: 0.00, 0.01, 0.05  
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT  
root     tty1                      Tue19    7:19   0.48s  0.48s -bash  
root     pts/3    192.168.30.1     08:47    7.00s  0.10s  0.00s w  
root     pts/4    192.168.30.1     08:49   23:27   0.02s  0.00s write root pts/3  
\[root@localhost pts\]\#  ***write root pts/4***  
please keep quit^H^H^H  
^C\[root@localhost pts\]\# ***lastlog***  
Username         Port     From             Latest  
root             pts/4    192.168.30.1     Thu Oct 26 08:49:56 +0800 2017  
bin                                        \*\*Never logged in\*\*  
daemon                                     \*\*Never logged in\*\*  
adm                                        \*\*Never logged in\*\*  
lp                                         \*\*Never logged in\*\*  
sync                                       \*\*Never logged in\*\*  
shutdown                                   \*\*Never logged in\*\*  
halt                                       \*\*Never logged in\*\*  
mail                                       \*\*Never logged in\*\*  
operator                                   \*\*Never logged in\*\*  
games                                      \*\*Never logged in\*\*  
ftp                                        \*\*Never logged in\*\*  
nobody                                     \*\*Never logged in\*\*  
systemd-network                            \*\*Never logged in\*\*  
dbus                                       \*\*Never logged in\*\*  
polkitd                                    \*\*Never logged in\*\*  
postfix                                    \*\*Never logged in\*\*  
sshd                                       \*\*Never logged in\*\*  
lzc                                        \*\*Never logged in\*\*  
\[root@localhost pts\]\# ***last***  
root     pts/4        192.168.30.1     Thu Oct 26 08:49   still logged in     
root     pts/3        192.168.30.1     Thu Oct 26 08:47   still logged in     
root     pts/2        192.168.30.1     Wed Oct 25 15:54 - 09:20  (17:26)     
root     tty1                          Tue Oct 24 19:32   still logged in     
reboot   system boot  3.10.0-693.el7.x Tue Oct 24 19:32 - 09:26 (1+13:53)    
wtmp begins Tue Oct 24 19:32:30 2017

$( )中放的是命令，相当于\` \`，例如todaydate=$(date +%Y%m%d)意思是执行date命令，返回执行结果给变量todaydate，也可以写为todaydate=\`date +%Y%m%d\`；

$\{ \}中放的是变量，例如echo $\{PATH\}取PATH变量的值并打印，也可以不加括号比如$PATH。

root@localhost ~\]\# echo $(date)  
Thu Oct 26 09:56:13 CST 2017  
\[root@localhost ~\]\# date +%F  
2017-10-26  
\[root@localhost ~\]\# date +%F -d 1day  
2017-10-27  
\[root@localhost ~\]\# date +%F -d -1day  
2017-10-25  
\[root@localhost ~\]\# \`date +%F\`  
\-bash: 2017-10-26: command not found  
\[root@localhost ~\]\# echo \`date\`  
Thu Oct 26 09:58:54 CST 2017  
\[root@localhost ~\]\# echo \`date +%F\`  
2017-10-26  
\[root@localhost ~\]\# echo \`date +%F\`todya  
2017-10-26todya

数组定义：用 a=（0 1 2 3），打印用 echo  $\{a\[1\]\}

2>&1和1> 2>的用法

\[root@localhost ~\]\# ls a***>test.f 2>&1***   
\[root@localhost ~\]\# cat test.f  
ls: cannot access a: No such file or directory  
\[root@localhost ~\]\# ls a     ***2>>test.f***  
\[root@localhost ~\]\# cat test.f  
ls: cannot access a: No such file or directory  
ls: cannot access a: No such file or directory  
  
  
**　孤儿进程：一个父进程退出，而它的一个或多个子进程还在运行，那么那些子进程将成为孤儿进程。孤儿进程将被init进程(进程号为1)所收养，并由init进程对它们完成状态收集工作。**

**　　僵尸进程：一个进程使用fork创建子进程，如果子进程退出，而父进程并没有调用wait或waitpid获取子进程的状态信息，那么子进程的进程描述符仍然保存在系统中。这种进程称之为僵死进程。**

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