Linux学习之计划任务(at、batch、crontab)篇

Linux学习之任务计划(at、batch、crontab)篇

一、linux上的任务计划
1、分类
linux上的任务计划可以分为两类：
a、周期性执行的任务计划
crontab
b、后续时间一次性执行的计划
at、batch
2、电子邮件服务
电子邮件服务使用到的几个协议：
smtp:simple mail transmission protocol
pop3:post office protocol
imap4:internet mail access protocol
没个用户的都有一个专门存放邮件的地方：
/var/spool/mail/USERNAME

[root@pizi mail]# ll
总用量 12
-rw-rw----. 1   3001 mail    0 9月   1 23:33 123user
-rw-r--r--. 1 root   root   11 9月   5 15:40 at.list
-rw-rw----. 1 hadoop mail    0 9月   5 11:01 hadoop
-rw-rw----. 1    600 mail    0 8月  27 00:40 piziuser
-rw-------. 1 root   mail 4773 9月   5 17:02 root
-rw-rw----. 1 rpc    mail    0 8月  24 23:03 rpc
-rw-rw----. 1 usera  mail    0 9月   4 20:23 usera
-rw-rw----. 1 userb  mail    0 9月   4 20:58 userb
-rw-rw----. 1 userc  mail    0 9月   4 20:58 userc
[root@pizi mail]#

mail命令：
mail：进入交互式收发邮件接口；

[root@pizi mail]# mail
Heirloom Mail version 12.4 7/29/08.  Type ? for help.
"/var/spool/mail/root": 5 messages
>   1 Mail Delivery System  Sat Sep  5 15:22  75/2399  "Undelivered Mail Retu"
2 usera@pizi.pizilinux  Sat Sep  5 15:23  19/557   "hi"
3 root                  Sat Sep  5 15:29  37/565   "Output from your job "
4 root                  Sat Sep  5 15:44  15/544   "Output from your job "
5 Cron Daemon           Sat Sep  5 16:30  23/708   "Cron <root@pizi> /bin"
&

mail -s 'SUBJECT' username@hostname

[root@pizi mail]# mail -s 'test mail' root@pizi.pizilinux
this is test mail
EOT
[root@pizi mail]# mail
Heirloom Mail version 12.4 7/29/08.  Type ? for help.
"/var/spool/mail/root": 10 messages 1 new
1 Mail Delivery System  Sat Sep  5 15:22  75/2399  "Undelivered Mail Retu"
2 usera@pizi.pizilinux  Sat Sep  5 15:23  19/557   "hi"
3 root                  Sat Sep  5 15:29  37/565   "Output from your job "
4 root                  Sat Sep  5 15:44  15/544   "Output from your job "
5 Cron Daemon           Sat Sep  5 16:30  23/708   "Cron <root@pizi> /bin"
6 Mail Delivery System  Tue Sep  8 22:33  75/2402  "Undelivered Mail Retu"
7 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
8 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
9 Mail Delivery System  Tue Sep  8 22:35  74/2324  "Undelivered Mail Retu"
>N 10 root                  Tue Sep  8 22:37  18/580   "test mail"
&

mail -s 'SUBJECT' username@hostname < /path/from/somefile

[root@pizi mail]# cat /tmp/testmail.txt
this is a test mail txt file!
[root@pizi mail]# mail -s 'txt' root@pizi.pizilinux < /tmp/testmail.txt
[root@pizi mail]# mail
Heirloom Mail version 12.4 7/29/08.  Type ? for help.
"/var/spool/mail/root": 11 messages 1 new 2 unread
1 Mail Delivery System  Sat Sep  5 15:22  75/2399  "Undelivered Mail Retu"
2 usera@pizi.pizilinux  Sat Sep  5 15:23  19/557   "hi"
3 root                  Sat Sep  5 15:29  37/565   "Output from your job "
4 root                  Sat Sep  5 15:44  15/544   "Output from your job "
5 Cron Daemon           Sat Sep  5 16:30  23/708   "Cron <root@pizi> /bin"
6 Mail Delivery System  Tue Sep  8 22:33  75/2402  "Undelivered Mail Retu"
7 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
8 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
9 Mail Delivery System  Tue Sep  8 22:35  74/2324  "Undelivered Mail Retu"
U 10 root                  Tue Sep  8 22:37  19/590   "test mail"
>N 11 root                  Tue Sep  8 22:41  18/586   "txt"
&
& 11
Message 11:
From root@pizi.pizilinux  Tue Sep  8 22:41:32 2015
Return-Path: <root@pizi.pizilinux>
X-Original-To: root@pizi.pizilinux
Delivered-To: root@pizi.pizilinux
Date: Tue, 08 Sep 2015 22:41:32 +0800
To: root@pizi.pizilinux
Subject: txt
User-Agent: Heirloom mailx 12.4 7/29/08
Content-Type: text/plain; charset=us-ascii
From: root@pizi.pizilinux (root)
Status: R

this is a test mail txt file!

&

COMMAND | mail -s 'SUBJECT' username@hostname

[root@pizi mail]# ifconfig | mail -s 'ifconfig' root@pizi.pizilinux
[root@pizi mail]# mail
Heirloom Mail version 12.4 7/29/08.  Type ? for help.
"/var/spool/mail/root": 12 messages 1 new 2 unread
1 Mail Delivery System  Sat Sep  5 15:22  75/2399  "Undelivered Mail Retu"
2 usera@pizi.pizilinux  Sat Sep  5 15:23  19/557   "hi"
3 root                  Sat Sep  5 15:29  37/565   "Output from your job "
4 root                  Sat Sep  5 15:44  15/544   "Output from your job "
5 Cron Daemon           Sat Sep  5 16:30  23/708   "Cron <root@pizi> /bin"
6 Mail Delivery System  Tue Sep  8 22:33  75/2402  "Undelivered Mail Retu"
7 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
8 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
9 Mail Delivery System  Tue Sep  8 22:35  74/2324  "Undelivered Mail Retu"
U 10 root                  Tue Sep  8 22:37  19/590   "test mail"
11 root                  Tue Sep  8 22:41  19/597   "txt"
>N 12 root                  Tue Sep  8 22:42  35/1448  "ifconfig"
& 12
Message 12:
From root@pizi.pizilinux  Tue Sep  8 22:42:58 2015
Return-Path: <root@pizi.pizilinux>
X-Original-To: root@pizi.pizilinux
Delivered-To: root@pizi.pizilinux
Date: Tue, 08 Sep 2015 22:42:57 +0800
To: root@pizi.pizilinux
Subject: ifconfig
User-Agent: Heirloom mailx 12.4 7/29/08
Content-Type: text/plain; charset=us-ascii
From: root@pizi.pizilinux (root)
Status: R

eth0      Link encap:Ethernet  HWaddr 08:00:27:A1:56:BC
inet addr:192.168.3.8  Bcast:192.168.3.255  Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:fea1:56bc/64 Scope:Link
UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
RX packets:1398 errors:0 dropped:0 overruns:0 frame:0
TX packets:975 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:135985 (132.7 KiB)  TX bytes:129159 (126.1 KiB)

3、at命令
at命令是承载未来时间运行的某作业：
支持使用作业队列：
默认为a队列；

使用方法：
at [option]... TIME
[option]选项
-q QUEUE ：at的作业队列；
-f /path/from/somefile:从指定的文件中读取要运行的作业；
-l：查看作业队列中德等待运行的作业，相当于使用atq命令；
-c AT JOB_NUM:查看待运行作业的内容
-d：删除指定作业；

TIME时间
a、绝对时间：
HH：MM，MMDD[CC]YY,MM/DD/[CC]/YY
b、相对时间：
now+#unit
unit:minute,hour,day,week
c、模糊时间：
midnight、noon、teatime

[root@pizi mail]# at now+1minute
at> ls /
at> <EOT>
job 4 at 2015-09-08 22:52
[root@pizi mail]# at -l
4       2015-09-08 22:52 a root

[root@pizi mail]# mail
Heirloom Mail version 12.4 7/29/08.  Type ? for help.
"/var/spool/mail/root": 13 messages 1 new 2 unread
1 Mail Delivery System  Sat Sep  5 15:22  75/2399  "Undelivered Mail Returned to Sender"
2 usera@pizi.pizilinux  Sat Sep  5 15:23  19/557   "hi"
3 root                  Sat Sep  5 15:29  37/565   "Output from your job        2"
4 root                  Sat Sep  5 15:44  15/544   "Output from your job        3"
5 Cron Daemon           Sat Sep  5 16:30  23/708   "Cron <root@pizi> /bin/echo "hello""
6 Mail Delivery System  Tue Sep  8 22:33  75/2402  "Undelivered Mail Returned to Sender"
7 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
8 usera@pizi.pizilinux  Tue Sep  8 22:34  19/567   "hi"
9 Mail Delivery System  Tue Sep  8 22:35  74/2324  "Undelivered Mail Returned to Sender"
U 10 root                  Tue Sep  8 22:37  19/590   "test mail"
11 root                  Tue Sep  8 22:41  19/597   "txt"
12 root                  Tue Sep  8 22:42  36/1459  "ifconfig"
>N 13 root                  Tue Sep  8 22:52  36/554   "Output from your job        4"
& 13
Message 13:
From root@pizi.pizilinux  Tue Sep  8 22:52:03 2015
Return-Path: <root@pizi.pizilinux>
X-Original-To: root
Delivered-To: root@pizi.pizilinux
Subject: Output from your job        4
To: root@pizi.pizilinux
Date: Tue,  8 Sep 2015 22:52:03 +0800 (CST)
From: root@pizi.pizilinux (root)
Status: R

bin
boot
dev
etc
home
lib
lib64
lost+found
media
misc
mnt
net
opt
proc
root
sbin
selinux
srv
sys
test
tmp
usr
var

4、batch：
由系统自行选择在资源较为空闲时运行指定的任务：

5、crontab：周期性的任务计划
其守护进程为crond

周期性任务计划分为两类：
a、系统cron任务：没有默认运行用户身份，所以需要额外指定运行者；

# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7)
# | | | | |
# * * * * * user-name command to be executed

系统性cron任务由7个字段组成：
前5个字段：时间点
user-name：计划时间点以哪个用户运行程序；
command to be executed:要运行的任务；

时间表示法：
*，表示该时间字段取值范围内的所有值
-：一个特定连续时间范围；3-7
,:一个离散的时间点，1,3,4,5
/#:有限时间范围内的每多少时间，用于指定频率；

注意：day of month ，month 两个时间点一般不与day of week同时使用

例：

[root@pizi mail]# crontab -l
5 */3 * * * root /bin/echo "hello world!"

表示每3个小时的第5分钟执行一次echo "hello world"命令

b、用户cron任务：由某个用户所提交，默认就是以提交者的身份运行，无需额外执行运行者：

# Example of job definition:# .---------------- minute (0 - 59)# | .------------- hour (0 - 23)# | | .---------- day of month (1 - 31)# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) # | | | | |# * * * * * command to be executed 此处的模式跟系统cron任务唯一不同的是此处不用指定运行用户了。其他都同上

c、crontab命令的用法：
crontab [-u user] [-l|-r|-e]
-u user:不是管理自己的cron任务，而是指定的目标用户的cron任务，仅root拥有管理其他用户的cron任务的权限，默认管理自己的；
-l：list 列出任务；
-r：remove，移除所有任务；
-e：edit，编辑，打开一当前shell回话的默认编辑器来编辑cron任务表；

d、注意：
1)、如果不想接收任务执行结果的通知邮件：
command > /dev/null :表示不接收执行任务正确的邮件通知
command &> /dev/null ：表示不接收所有的邮件通知
2)、对于crontab文件来讲，%有特殊的功用，如果命令中出现了%，要记得转义，或者用单引号对其引用；
3)、crondtab的path变量与用户的变量不完全相同，所以建议在cron中的任务要使用绝对路径来执行

二、练习：
1、每周一到周六的凌晨3点20分，运行cp命令对/etc/目录进行归档另存，存储位置为/backups/etc-YYYY-MM-DD;

[root@pizi backups]# crontab -l
20 3 * * 1-6 /bin/cp -af /etc/ /backups/etc-$(date +\%F)

2、每周日凌晨2点30分，运行cp命令对/etc/fstab文件进行备份，存储位置为/backup/fstab-YYYY-MM-DD-hh-mm-ss

[root@pizi backups]# crontab -l
20 3 * * 1-6 /bin/cp -af /etc/ /backups/etc-$(date +\%F)
30 2 * * 0 /bin/cp -af /etc/fstab /backups/fstab-$(date +\%F-\%H-\%M-\%S)

3、每天晚上12点，取得/proc/meminfo文件中所有以S或M开头的行，追加至/statistics/meminfo.txt文件中，且每天的消息之前，要加上类似===============分隔线；

[root@pizi statistics]# crontab -l
20 3 * * 1-6 /bin/cp -af /etc/ /backups/etc-$(date +\%F)
30 2 * * 0 /bin/cp -af /etc/fstab /backups/fstab-$(date +\%F-\%H-\%M-\%S)
0 23 * * * (/bin/echo "============";/bin/egrep "^(S|M)" /proc/meminfo) >> /statistics/meminfo.txt