Linux timed task

Posted 2020-12-11 nedrain

at

if not, Start Atd Service

systemctl status atd.service
//output:
┌─[root@nedrain]─[~]
└──? $systemctl status atd.service
● atd.service - Job spooling tools
   Loaded: loaded (/usr/lib/systemd/system/atd.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2020-06-16 10:51:39 CST; 2 days ago
 Main PID: 468 (atd)
   CGroup: /system.slice/atd.service
           └─468 /usr/sbin/atd -f

Jun 16 10:51:39 localhost.localdomain systemd[1]: Started Job spooling tools.
Jun 16 10:51:39 localhost.localdomain systemd[1]: Starting Job spooling tools...
Hint: Some lines were ellipsized, use -l to show in full.
// if the service not running, use "systemctl start atd.service" to start the service

/etc/at.allow ? /etc/at.deny (the .allow file has priority)

//if none of those two file exists, only root can use command "at"

at [option] [time]

// example of time formation
// HH:MM  02:30
// HH:MM YYYY-MM-DD 02:30 2013-07-25
// HH:MM  + [minutes | hours | days | weeks]  now + 5 minutes, 05am + 2 hours

┌─[root@nedrain]─[~]
└──? $at now + 2 minutes  // this is at command
at> echo "hello">/root/a.txt
at> <EOT>              // use ctrl + d to end the input
job 6 at Fri Jun 19 11:15:00 2020   // here‘s the output

atq (look up the timing tasks roughly)

┌─[root@nedrain]─[~]
└──? $atq
6	Fri Jun 19 11:15:00 2020 a root

at -c [task number] ( for details)

┌─[root@nedrain]─[~]
└──? $at -c 6
#!/bin/sh
# atrun uid=0 gid=0
# mail root 0
umask 22
XDG_SESSION_ID=546; export XDG_SESSION_ID
HOSTNAME=nedrain; export HOSTNAME
SHELL=/bin/bash; export SHELL
HISTSIZE=1000; export HISTSIZE
SSH_CLIENT=223.104.37.171 27695 22; export SSH_CLIENT
SSH_TTY=/dev/pts/0; export SSH_TTY
LC_ALL=en_US.UTF-8; export LC_ALL
USER=root; export USER
LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=01;05;37;41:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.axv=01;35:*.anx=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=01;36:*.au=01;36:*.flac=01;36:*.mid=01;36:*.midi=01;36:*.mka=01;36:*.mp3=01;36:*.mpc=01;36:*.ogg=01;36:*.ra=01;36:*.wav=01;36:*.axa=01;36:*.oga=01;36:*.spx=01;36:*.xspf=01;36:; export LS_COLORS
MAIL=/var/spool/mail/root; export MAIL
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin; export PATH
PWD=/root; export PWD
LANG=en_US.UTF-8; export LANG
PS1=\[\033[0;31m\]\342\224\214\342\224\200[\[\033[0;39m\]\u\[\033[01;33m\]@\[\033[01;96m\]\h\[\033[0;31m\]]\342\224\200[\[\033[0;32m\]\w\[\033[0;31m\]]\n\[\033[0;31m\]\342\224\224\342\224\200\342\224\200\342\225\274 \[\033[0m\]\[\e[01;33m\]$\[\e[0m\]; export PS1
HISTCONTROL=ignoredups; export HISTCONTROL
SHLVL=1; export SHLVL
HOME=/root; export HOME
LOGNAME=root; export LOGNAME
SSH_CONNECTION=223.104.37.171 27695 172.19.4.50 22; export SSH_CONNECTION
LC_CTYPE=UTF-8; export LC_CTYPE
LESSOPEN=||/usr/bin/lesspipe.sh %s; export LESSOPEN
XDG_RUNTIME_DIR=/run/user/0; export XDG_RUNTIME_DIR
cd /root || {
	 echo ‘Execution directory inaccessible‘ >&2
	 exit 1
}
${SHELL:-/bin/sh} << ‘marcinDELIMITER65959aa8‘
echo "hello">/root/a.txt      // only this line is your code

marcinDELIMITER65959aa8

cron

also first start your crond service (if not started)

//

also, file /etc/cron.allow & file /etc/cron.deny

┌─[root@nedrain]─[~]
└──? $ls /etc/cron*
/etc/cron.deny  /etc/crontab

/etc/cron.d:
0hourly  sysstat

/etc/cron.daily:
logrotate  man-db.cron

/etc/cron.hourly:
0anacron

/etc/cron.monthly:

/etc/cron.weekly:

crontab -e [task]

// here is the file /etc/crontab
/*
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# 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) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed */

// there are special symbols
// * means random time , so "* * * * *" will let the command execute every minute
// */n means executing command every n minutes
// 0 8, 12, 16 * * * means executing command at 08:00 and 12:00 and 16:00
// 0 5 * * 1-6 means executing command at 05:00 from Monday to Saturday
 

crontab -e
//* * * * * root echo 1111 >> /root/a.txt   // this is a wrong example, don‘t add a root 
* * * * * echo 1111 >> /root/a.txt

 
// use "crontab -l " to query
┌─[root@nedrain]─[~]
└──? $crontab -l
* * * * *  echo 1111 > /root/a.txt

and if you wanna change , keep using "crontab -e" to edit, or use "crontab -r" to remove all

/etc/crontab (RECOMMENDED)

if you use "crontab -e", you can‘t let others do the task, but by editing /etc/crontab, you can let others do the job for you

// here is the file /etc/crontab
/*
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# 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) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed */