69 Moving a Process to the Foreground If you want to move a process running in the background to the fore
ground, you can use the
fg
(foreground) command. The
fg
command
requires the PID of the process you want to return to the foreground, as
shown next.
kali >
fg 1234 If you don’t know the PID, you can use the
ps
command to find it.
Scheduling Processes Both Linux system administrators and hackers often need to schedule
processes to run at a particular time of day. A system administrator might
want to schedule a system backup to run every Saturday night at 2
am
, for
example. A hacker might want to set a script to run to perform reconnais
sance on a regular basis, finding open ports or vulnerabilities. In Linux,
you can accomplish this in at least two ways: with
at
and
crond
.
The
at
command is used to set up the daemon—a background process—
atd
, which is useful for scheduling a job to run once at some point in the
future. The
crond
daemon is more suited for scheduling tasks to occur every
day, week, or month, and we’ll cover this in detail in Chapter 16.
We use the
at
daemon to schedule the execution of a command or set
of commands in the future. The syntax is simply the
at
command followed
by the time to execute the process. The time argument can be provided in
various formats. Table 62 contains the most common
at
time formats.
Table 6-2:
Time Formats Accepted by the
at
Command
Time format
Meaning
at 7:20pm
Scheduled to run at 7:20
pm
on the current day
at 7:20pm June 25
Scheduled to run at 7:20
pm
on June 25
at noon
Scheduled to run at noon on the current day
at noon June 25
Scheduled to run at noon on June 25
at tomorrow
Scheduled to run tomorrow
at now + 20 minutes
Scheduled to run in 20 minutes from the current time
at now + 10 hours
Scheduled to run in 10 hours from the current time
at now + 5 days
Scheduled to run in five days from the current date
at now + 3 weeks
Scheduled to run in three weeks from the current date
at 7:20pm 06/25/2019
Scheduled to run at 7:20
pm
on June 25, 2019
70 Chapter 6
When you enter the
at
daemon with the specified time,
at
goes into
interactive mode and you are greeted with an
at>
prompt. Here is where
you enter the command you want executed at the specified time:
kali >
