at命令用于在指定时间执行命令。at允许使用一套相当复杂的指定时间的方法。可以用相对时间法指定，也可以用绝对时间法指定。
(1)用法:
用法: at [选项参数] [时间]
(2)功能:
功能: 在指定的时间执行命令。
(3)选项参数:
1) -c 显示即将执行任务的细节
2) -d 用任务id号删除指定的任务
3) -l 等同于atq，用job的id号显示指定的未删除而待执行的任务
(4)实例:
1)[root@localhost sunjimeng]# at now + 1 minutes 用相对时间，在一分钟之后执行命令
[root@localhost sunjimeng]# at now + 2 minutes
at> echo "I'm MenAngel!,I'm study at order!"
at> <EOT>
job 11 at Wed Jun 8 17:46:00 2016
at> <EOT>
<这里输入 [ctrl] + d 就会出现 <EOF> 的字样代表结束!
当你输入下一个命令时，系统会自动提醒你，您在 /var/spool/mail/sunjimeng 中有邮件。此邮件中就包含这个命令执行的结果。
2)[root@localhost sunjimeng]# at 17:47 在一个绝对时间执行一个命令
[root@localhost sunjimeng]# at 17:47 at> ls -l /home/sunjimeng/Documents at> <EOT> job 13 at Wed Jun 8 17:47:00 2016 您在 /var/spool/mail/sunjimeng 中有新邮件
这里在语句的末尾提醒你有新邮件，可以用cat命令查看文件:/var/spool/mail/sunjimeng。
3)[root@localhost sunjimeng]# atq 计划任务设定后，在没有执行之前我们可以用atq命令来查看系统没有执行工作任务
[root@localhost sunjimeng]# atq 1 Wed Jun 8 17:21:00 2016 a root 2 Wed Jun 8 17:23:00 2016 a root 3 Wed Jun 8 17:23:00 2016 a root 4 Wed Jun 8 17:26:00 2016 a root 5 Sat Jun 11 17:00:00 2016 a root 6 Wed Jun 8 17:31:00 2016 a root
4)[root@localhost sunjimeng]# atq 删除已经设置的任务
[root@localhost sunjimeng]# atq 1 Wed Jun 8 17:21:00 2016 a root 2 Wed Jun 8 17:23:00 2016 a root 3 Wed Jun 8 17:23:00 2016 a root 4 Wed Jun 8 17:26:00 2016 a root 5 Sat Jun 11 17:00:00 2016 a root 6 Wed Jun 8 17:31:00 2016 a root [root@localhost sunjimeng]# atrm 1 2 3 4 5 [root@localhost sunjimeng]# atq 6 Wed Jun 8 17:31:00 2016 a root
5)[root@localhost sunjimeng]# cat /var/spool/mail/sunjimeng 显示at命令的执行结果
[root@localhost sunjimeng]# cat /var/spool/mail/sunjimeng From root@localhost.localdomain Wed Jun 8 17:46:01 2016 Return-Path: <root@localhost.localdomain> X-Original-To: sunjimeng Delivered-To: sunjimeng@localhost.localdomain Received: by localhost.localdomain (Postfix, from userid 0) id 24622632F338; Wed, 8 Jun 2016 17:46:01 -0700 (PDT) Subject: Output from your job 11 To: sunjimeng@localhost.localdomain Message-Id: <20160609004601.24622632F338@localhost.localdomain> Date: Wed, 8 Jun 2016 17:46:01 -0700 (PDT) From: root@localhost.localdomain (root) I'm MenAngel!,I'm study at order! From root@localhost.localdomain Wed Jun 8 17:47:00 2016 Return-Path: <root@localhost.localdomain> X-Original-To: sunjimeng Delivered-To: sunjimeng@localhost.localdomain Received: by localhost.localdomain (Postfix, from userid 0) id C83A5632F338; Wed, 8 Jun 2016 17:47:00 -0700 (PDT) Subject: Output from your job 13 To: sunjimeng@localhost.localdomain Message-Id: <20160609004700.C83A5632F338@localhost.localdomain> Date: Wed, 8 Jun 2016 17:47:00 -0700 (PDT) From: root@localhost.localdomain (root) 总用量 0 drwxr-xr-x. 2 root root 72 5月 31 18:25 grepDir -rw-r--r--. 1 root root 0 6月 7 23:34 myfile drwxr-xr-x. 2 root root 6 6月 7 23:33 newWatch From root@localhost.localdomain Wed Jun 8 17:47:00 2016 Return-Path: <root@localhost.localdomain> X-Original-To: sunjimeng Delivered-To: sunjimeng@localhost.localdomain Received: by localhost.localdomain (Postfix, from userid 0) id C9EA3632F33A; Wed, 8 Jun 2016 17:47:00 -0700 (PDT) Subject: Output from your job 12 To: sunjimeng@localhost.localdomain Message-Id: <20160609004700.C9EA3632F33A@localhost.localdomain> Date: Wed, 8 Jun 2016 17:47:00 -0700 (PDT) From: root@localhost.localdomain (root) 总用量 0 drwxr-xr-x. 2 root root 72 5月 31 18:25 grepDir -rw-r--r--. 1 root root 0 6月 7 23:34 myfile drwxr-xr-x. 2 root root 6 6月 7 23:33 newWatch From root@localhost.localdomain Wed Jun 8 17:52:01 2016 Return-Path: <root@localhost.localdomain> X-Original-To: sunjimeng Delivered-To: sunjimeng@localhost.localdomain Received: by localhost.localdomain (Postfix, from userid 0) id F3239632F338; Wed, 8 Jun 2016 17:52:00 -0700 (PDT) Subject: Output from your job 14 To: sunjimeng@localhost.localdomain Message-Id: <20160609005200.F3239632F338@localhost.localdomain> Date: Wed, 8 Jun 2016 17:52:00 -0700 (PDT) From: root@localhost.localdomain (root) I'm MenAngel From root@localhost.localdomain Wed Jun 8 17:54:00 2016 Return-Path: <root@localhost.localdomain> X-Original-To: sunjimeng Delivered-To: sunjimeng@localhost.localdomain Received: by localhost.localdomain (Postfix, from userid 0) id 4B264632F338; Wed, 8 Jun 2016 17:54:00 -0700 (PDT) Subject: Output from your job 15 To: sunjimeng@localhost.localdomain Message-Id: <20160609005400.4B264632F338@localhost.localdomain> Date: Wed, 8 Jun 2016 17:54:00 -0700 (PDT) From: root@localhost.localdomain (root) 总用量 4 drwxr-xr-x. 2 sunjimeng sunjimeng 6 5月 1 01:23 Desktop drwxrwxr-x. 4 sunjimeng users 4096 5月 28 00:24 Document drwxr-xr-x. 4 root sunjimeng 48 6月 7 23:34 Documents drwxr-xr-x. 2 sunjimeng sunjimeng 6 5月 1 01:23 Downloads drwxrwxr-x. 2 sunjimeng sunjimeng 6 5月 17 04:55 findTextDir drwxr-xr-x. 2 sunjimeng sunjimeng 6 5月 1 01:23 Music drwxr-xr-x. 2 sunjimeng sunjimeng 6 5月 1 01:23 Pictures drwxr-xr-x. 2 sunjimeng sunjimeng 6 5月 1 01:23 Public drwxr-xr-x. 2 sunjimeng sunjimeng 6 5月 1 01:23 Templates drwxr-xr-x. 2 sunjimeng sunjimeng 6 5月 1 01:23 Videos From root@localhost.localdomain Wed Jun 8 17:54:00 2016 Return-Path: <root@localhost.localdomain> X-Original-To: sunjimeng Delivered-To: sunjimeng@localhost.localdomain Received: by localhost.localdomain (Postfix, from userid 0) id 4E5D2632F33A; Wed, 8 Jun 2016 17:54:00 -0700 (PDT) Subject: Output from your job 16 To: sunjimeng@localhost.localdomain Message-Id: <20160609005400.4E5D2632F33A@localhost.localdomain> Date: Wed, 8 Jun 2016 17:54:00 -0700 (PDT) From: root@localhost.localdomain (root) 总用量 0 drwxr-xr-x. 2 root root 72 5月 31 18:25 grepDir -rw-r--r--. 1 root root 0 6月 7 23:34 myfile drwxr-xr-x. 2 root root 6 6月 7 23:33 newWatch
6)[sunjimeng@localhost ~]$ at -c 18 根据id号查看即将要执行命令的细节
[sunjimeng@localhost ~]$ atq //显示结果表明没有即将要执行的任务 [sunjimeng@localhost ~]$ at now + 1 minutes //新建一个要执行的任务 at> ls -l at> <EOT> job 18 at Wed Jun 8 18:09:00 2016 [sunjimeng@localhost ~]$ atq //查看 18 Wed Jun 8 18:09:00 2016 a sunjimeng [sunjimeng@localhost ~]$ at -c 18 //根据id号查看，它的即将执行的细节 #!/bin/sh # atrun uid=1000 gid=1000 # mail sunjimeng 0 umask 2 XDG_VTNR=1; export XDG_VTNR SSH_AGENT_PID=3132; export SSH_AGENT_PID XDG_SESSION_ID=2; export XDG_SESSION_ID HOSTNAME=localhost.localdomain; export HOSTNAME IMSETTINGS_INTEGRATE_DESKTOP=yes; export IMSETTINGS_INTEGRATE_DESKTOP GPG_AGENT_INFO=/run/user/1000/keyring-CchymL/gpg:0:1; export GPG_AGENT_INFO VTE_VERSION=3406; export VTE_VERSION SHELL=/bin/bash; export SHELL XDG_MENU_PREFIX=gnome-; export XDG_MENU_PREFIX HISTSIZE=1000; export HISTSIZE GJS_DEBUG_OUTPUT=stderr; export GJS_DEBUG_OUTPUT WINDOWID=25197065; export WINDOWID GNOME_KEYRING_CONTROL=/run/user/1000/keyring-CchymL; export GNOME_KEYRING_CONTROL GJS_DEBUG_TOPICS=JS ERROR;JS LOG; export GJS_DEBUG_TOPICS IMSETTINGS_MODULE=IBus; export IMSETTINGS_MODULE USER=sunjimeng; export USER LS_COLORS=rs=0:di=38;5;27:ln=38;5;51:mh=44;38;5;15:pi=40;38;5;11:so=38;5;13:do=38;5;5:bd=48;5;232;38;5;11:cd=48;5;232;38;5;3:or=48;5;232;38;5;9:mi=05;48;5;232;38;5;15:su=48;5;196;38;5;15:sg=48;5;11;38;5;16:ca=48;5;196;38;5;226:tw=48;5;10;38;5;16:ow=48;5;10;38;5;21:st=48;5;21;38;5;15:ex=38;5;34:*.tar=38;5;9:*.tgz=38;5;9:*.arc=38;5;9:*.arj=38;5;9:*.taz=38;5;9:*.lha=38;5;9:*.lz4=38;5;9:*.lzh=38;5;9:*.lzma=38;5;9:*.tlz=38;5;9:*.txz=38;5;9:*.tzo=38;5;9:*.t7z=38;5;9:*.zip=38;5;9:*.z=38;5;9:*.Z=38;5;9:*.dz=38;5;9:*.gz=38;5;9:*.lrz=38;5;9:*.lz=38;5;9:*.lzo=38;5;9:*.xz=38;5;9:*.bz2=38;5;9:*.bz=38;5;9:*.tbz=38;5;9:*.tbz2=38;5;9:*.tz=38;5;9:*.deb=38;5;9:*.rpm=38;5;9:*.jar=38;5;9:*.war=38;5;9:*.ear=38;5;9:*.sar=38;5;9:*.rar=38;5;9:*.alz=38;5;9:*.ace=38;5;9:*.zoo=38;5;9:*.cpio=38;5;9:*.7z=38;5;9:*.rz=38;5;9:*.cab=38;5;9:*.jpg=38;5;13:*.jpeg=38;5;13:*.gif=38;5;13:*.bmp=38;5;13:*.pbm=38;5;13:*.pgm=38;5;13:*.ppm=38;5;13:*.tga=38;5;13:*.xbm=38;5;13:*.xpm=38;5;13:*.tif=38;5;13:*.tiff=38;5;13:*.png=38;5;13:*.svg=38;5;13:*.svgz=38;5;13:*.mng=38;5;13:*.pcx=38;5;13:*.mov=38;5;13:*.mpg=38;5;13:*.mpeg=38;5;13:*.m2v=38;5;13:*.mkv=38;5;13:*.webm=38;5;13:*.ogm=38;5;13:*.mp4=38;5;13:*.m4v=38;5;13:*.mp4v=38;5;13:*.vob=38;5;13:*.qt=38;5;13:*.nuv=38;5;13:*.wmv=38;5;13:*.asf=38;5;13:*.rm=38;5;13:*.rmvb=38;5;13:*.flc=38;5;13:*.avi=38;5;13:*.fli=38;5;13:*.flv=38;5;13:*.gl=38;5;13:*.dl=38;5;13:*.xcf=38;5;13:*.xwd=38;5;13:*.yuv=38;5;13:*.cgm=38;5;13:*.emf=38;5;13:*.axv=38;5;13:*.anx=38;5;13:*.ogv=38;5;13:*.ogx=38;5;13:*.aac=38;5;45:*.au=38;5;45:*.flac=38;5;45:*.mid=38;5;45:*.midi=38;5;45:*.mka=38;5;45:*.mp3=38;5;45:*.mpc=38;5;45:*.ogg=38;5;45:*.ra=38;5;45:*.wav=38;5;45:*.axa=38;5;45:*.oga=38;5;45:*.spx=38;5;45:*.xspf=38;5;45:; export LS_COLORS SSH_AUTH_SOCK=/run/user/1000/keyring-CchymL/ssh; export SSH_AUTH_SOCK SESSION_MANAGER=local/unix:@/tmp/.ICE-unix/2990,unix/unix:/tmp/.ICE-unix/2990; export SESSION_MANAGER USERNAME=sunjimeng; export USERNAME GNOME_SHELL_SESSION_MODE=classic; export GNOME_SHELL_SESSION_MODE PATH=/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:/home/sunjimeng/.local/bin:/home/sunjimeng/bin; export PATH MAIL=/var/spool/mail/sunjimeng; export MAIL DESKTOP_SESSION=gnome-classic; export DESKTOP_SESSION QT_IM_MODULE=ibus; export QT_IM_MODULE PWD=/home/sunjimeng; export PWD XMODIFIERS=@im=ibus; export XMODIFIERS GNOME_KEYRING_PID=2967; export GNOME_KEYRING_PID LANG=zh_CN.utf8; export LANG GDM_LANG=zh_CN.utf8; export GDM_LANG GDMSESSION=gnome-classic; export GDMSESSION HISTCONTROL=ignoredups; export HISTCONTROL XDG_SEAT=seat0; export XDG_SEAT HOME=/home/sunjimeng; export HOME SHLVL=2; export SHLVL GNOME_DESKTOP_SESSION_ID=this-is-deprecated; export GNOME_DESKTOP_SESSION_ID LOGNAME=sunjimeng; export LOGNAME DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-O0naLUCbYg,guid=ad8d9a1bab9eccd8c11d0a6257493a83; export DBUS_SESSION_BUS_ADDRESS LESSOPEN=||/usr/bin/lesspipe.sh %s; export LESSOPEN WINDOWPATH=1; export WINDOWPATH XDG_RUNTIME_DIR=/run/user/1000; export XDG_RUNTIME_DIR COLORTERM=gnome-terminal; export COLORTERM XAUTHORITY=/run/gdm/auth-for-sunjimeng-Bcg9Bg/database; export XAUTHORITY cd /home/sunjimeng || { echo 'Execution directory inaccessible' >&2 exit 1 } ${SHELL:-/bin/sh} << 'marcinDELIMITER7e20521d' ls -l marcinDELIMITER7e20521d [sunjimeng@localhost ~]$
7)[sunjimeng@localhost ~]$ at -d 21 取消指向执行id号为21的任务
[sunjimeng@localhost ~]$ atq 20 Wed Jun 8 18:15:00 2016 a sunjimeng 21 Wed Jun 8 18:16:00 2016 a sunjimeng [sunjimeng@localhost ~]$ atrm 20 [sunjimeng@localhost ~]$ atq 21 Wed Jun 8 18:16:00 2016 a sunjimeng [sunjimeng@localhost ~]$ at -d 21 [sunjimeng@localhost ~]$ atq