Schedulare attività su Linux con at

Per schedulare attività e operazioni su Linux, oltre al classico e famoso cron, abbiamo anche il comando at.

Sulla mia Debian era già installato di default; se non lo fosse:

# aptitude install at

Su Arch Linux:

# pacman -Sy at

Cominciamo con un esempio semplice:

$ at now + 2 minutes
warning: commands will be executed using /bin/sh
at> echo ciao
at> <EOT>
job 2 at Wed Jun 19 10:02:00 2019

Nel primo at> dovete scrivere quello che deve essere eseguito; una volta fatto tutto date CTRL+D per uscire e salvare.

Per vedere i job attivi:

$ atq
2	Wed Jun 19 10:02:00 2019 a root

Per vedere il dettaglio di un job:

$ at -c 2
#!/bin/sh
# atrun uid=0 gid=0
# mail matte 0
umask 22
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=00: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:*.zst=01;31:*.tzst=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:*.mjpg=01;35:*.mjpeg=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:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:; export LS_COLORS
XDG_MENU_PREFIX=xfce-; export XDG_MENU_PREFIX
LANG=it_IT.UTF-8; export LANG
COLORTERM=truecolor; export COLORTERM
XDG_VTNR=7; export XDG_VTNR
SSH_AUTH_SOCK=/tmp/ssh-nXOqJ30NRehy/agent.2890; export SSH_AUTH_SOCK
GLADE_CATALOG_PATH=:; export GLADE_CATALOG_PATH
XDG_SESSION_ID=1; export XDG_SESSION_ID
XDG_GREETER_DATA_DIR=/var/lib/lightdm/data/matte; export XDG_GREETER_DATA_DIR
USER=root; export USER
GLADE_MODULE_PATH=:; export GLADE_MODULE_PATH
DESKTOP_SESSION=lightdm-xsession; export DESKTOP_SESSION
QT_QPA_PLATFORMTHEME=gtk2; export QT_QPA_PLATFORMTHEME
PWD=/home/matte; export PWD
HOME=/root; export HOME
SSH_AGENT_PID=2976; export SSH_AGENT_PID
QT_ACCESSIBILITY=1; export QT_ACCESSIBILITY
XDG_SESSION_TYPE=x11; export XDG_SESSION_TYPE
QT_PLATFORM_PLUGIN=gtk2; export QT_PLATFORM_PLUGIN
XDG_DATA_DIRS=/usr/share/xfce4:/home/matte/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/share:/usr/share; export XDG_DATA_DIRS
XDG_SESSION_DESKTOP=lightdm-xsession; export XDG_SESSION_DESKTOP
GLADE_PIXMAP_PATH=:; export GLADE_PIXMAP_PATH
GTK_MODULES=canberra-gtk-module; export GTK_MODULES
MAIL=/var/mail/root; export MAIL
VTE_VERSION=4601; export VTE_VERSION
XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0; export XDG_SEAT_PATH
XDG_CURRENT_DESKTOP=XFCE; export XDG_CURRENT_DESKTOP
QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1; export QT_LINUX_ACCESSIBILITY_ALWAYS_ON
SHLVL=3; export SHLVL
XDG_SEAT=seat0; export XDG_SEAT
WINDOWID=71303171; export WINDOWID
GDMSESSION=lightdm-xsession; export GDMSESSION
LOGNAME=root; export LOGNAME
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-tuDQYDZeVq,guid=8d3a99460f7cf697afc8a4e45d09e8c7; export DBUS_SESSION_BUS_ADDRESS
XDG_RUNTIME_DIR=/run/user/1000; export XDG_RUNTIME_DIR
XAUTHORITY=/home/matte/.Xauthority; export XAUTHORITY
XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0; export XDG_SESSION_PATH
XDG_CONFIG_DIRS=/etc/xdg; export XDG_CONFIG_DIRS
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin; export PATH
QT_PLATFORMTHEME=gtk2; export QT_PLATFORMTHEME
SESSION_MANAGER=local/mstte-mx:@/tmp/.ICE-unix/2988,unix/mstte-mx:/tmp/.ICE-unix/2988; export SESSION_MANAGER
cd /home/matte || {
	 echo 'Execution directory inaccessible' >&2
	 exit 1
}
echo ciao

È possibile anche eseguire operazioni / programmi grafici; prima di tutto visualiziamo il display corrente:

$ echo $DISPLAY
:0.0

Adesso diciamo di avviare Firefox:

$ at now + 2 minutes
warning: commands will be executed using /bin/sh
at> export DISPLAY=:0.0
at> firefox
at> <EOT>
job 4 at Wed Jun 19 10:05:00 2019

$ atq
4	Wed Jun 19 10:05:00 2019 a matte

Aspettate due minuti per l'avvio del programma.

Ovviamente sono esempi basici, ma vi fa comprendere come può essere più comodo di cron in certi casi; ad esempio se volete creare un scheduler al volo da eseguire una volta ad un determinata ora (ad esempio una operazione sul server).

Enjoy!