Scheduling Flashcards
atd vs crond
atd: onet ime jobs
crond: recurring jobs
Which commands to use to schedule jobs
one off: at
recurring: crontab
Determine which jobs are schedule for one time execute
atq
remove an at job
atrm 2
Can’t open /run/atd.pid to signal atd. No atd running?
Install atd
Schedule an AT job for 5 min from now
at now +5min
teatime
4pm
Execute command at teatime and put the job in a queue called g
at -q g teatime
Cat an at job to the console
at -c 7
In order, list the fields of a cron job
minute
hour
day of month
month
day of week
command
In cron, what are values for day of the week?
0, 7 for Sunday
1 for Monday
true command
do nothing and return success code 0
false command
do nothing and return success code of 1
List the cron tabs
crontab -l
Install cron
dnf install cronie
Create a cron job
crontab -e
source fancy dot command
. ~/.bashrc
Explain the crontab:
15,45 08,11,14 * * 1-5 /bin/true
At 15 min or 45 min after 08, 11 or 1pm, any day of the month and for every month for working days, run /bin/true
Explain the cron tab:
*/10 * * * * /bin/true
Every tenth instance of every hour, every day of month, every month, every day of the week
List the crontabs of student user
crontab -l -u student
Where are cront tab installed
/var/spool/cron
remove the crontab for student user
crontab -r -u student
How many fields are used for user cron tabs?
6: min, hour, day of month, month, day of week command
How many fields are used for system cron tabs?
7
additional field for the suer that the job is going to be executed as
Where can I find information on the cron tab fileds?
/etc/crontab
Where do I get help on system cron tabs?
man 5 crontab
What is the cron drop in directory
/etc/cron.d
Explain run‐parts command
command used to run all the executable scripts or programs in a directory in alphabetical order.
Anacron
scheduling tasks to be executed periodicallyin systems not always on. Or when you do not care about precise executime time (daily, weekly, hourly).
What are the anacron drop in directory
1) /etc/cron.hourly/,
2) /etc/cron.weekly/,
3) /etc/cron.daily/
4) /etc/cron.monthy/
what is anacrontab?
The anacrontab file in Linux is a configuration file for the Anacron service. It specifies how often Anacron runs certain tasks, much like a crontab file for Cron
Explain nice command
nice is used to run a program with modified scheduling priority. By default, programs run with a normal priority level, but nice allows you to start a program with a lower priority, so that it uses less CPU resources.
Setup anacron job to update locate database every hour
echo 'updatedb' > /etc/cron.hourly/locate
List all systemd timer units
systemctl list-units --type timer
Explain: w -h
w with no header
How do you reload systemd after changing some units?
systemctl daemon-reload
Enable a timer unit that was recently installed
systemctl enable –now sysstat-collect.timer
Explain:
crontab filename
Replace all jobs with those read from filename. This command uses stdin input when no file is specified.
How do you set who should receive the output of cron job execution?
Set MAILTO var in crontab file
You want crond to run a command that requires data via stdin. How do you set it up?
Separate the command (inc its arguments) with the stdin data with percent sign
A cron job writes to stdout. What happens with this output?
if MAILTO is configured it is sent to the specified user.
Otherwise if it is a system job, it is sent to root.
And else, it is send to the job owner.
Instruct you shell to sleep until a file is created
while ! test -f filename.txt; do sleep 1s; done
remove all cron jobs
crontab -r
What do you put in following folders?
/etc/cron.daily/ /etc/cron.weekly/ /etc/cron.monthly/
bash files with execute permission
What are the fields of an anacron tab entry?
1) perdiod in days (1: for daily, 7 for weekly, @monthly)
2) period in minutes
3) job id
4) command
Explain “Delay in minutes” in anacrontab
the time that the crond daemon must wait before it starts the job.
Parameters that determine when anacron job will be run
1) RANDOM_DELAY
2) START_HOURS_RANGE
3) Delay in minutes
Install sysstat package
dnf install sysstat
What is sysstat
A unit that collects system stats regularly (by default 10 min)
