A technique for scheduling tasks to be run at a specific time or on a specific event.

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67
votes
8answers
148k views

Where are cron errors logged?

If I setup cron jobs incorrectly they appear to silently fail. Where should I look for an error log to understand what went wrong?
54
votes
3answers
199k views

How can get a list of all scheduled cron jobs on my machine?

My sysadmin has set up a bunch of cron jobs on my machine. I'd like to know exactly what is scheduled for what time. How can I get that list?
24
votes
1answer
3k views

High CPU usage with CFS?

I asked a previous question to try and isolate the source of an increase in CPU usage when moving an application from RHEL 5 to RHEL 6. The analysis that I did for that seems to indicate that it is ...
21
votes
3answers
53k views

How to shutdown Linux at a specific datetime from terminal?

It seems I can shutdown using sudo shutdown by specifying a time or minutes. Is there a way to specify datetime for shutdown?
19
votes
2answers
427 views

Why does niceness range from -20 to 19?

The nice command allows you to adjust the scheduling priority ("niceness") of a program. On all Unix-like systems I've used, niceness is specified by a range of integers, where -20 is the most ...
15
votes
1answer
3k views

How is nice working?

sched_setscheduler says : All scheduling is preemptive: if a process with a higher static priority becomes ready to run, the currently running process will be preempted and ...
14
votes
2answers
1k views

What is a simple way to schedule a single event to happen at some time in the future?

There are often times that I want my computer to do a single task, but not right now. For example, I could have it notify me in 30 minutes that it is time to leave work. Or maybe I want it to run a ...
11
votes
2answers
12k views

Bash Script on Startup? (Linux)

Is there any way to make/run a bash script on reboot (like in Debian/Ubuntu for instance, since thats what my 2 boxes at home have) Also, any recommended guides for doing cron jobs? I'm completely ...
11
votes
1answer
3k views

How do I view the IO priority of a process?

How can I view the IO priority of a process? like to see for example if something has been ionice-ed.
11
votes
1answer
8k views

Real time processes scheduling in Linux

I have been learning some scheduling concepts. Currently my understanding so far is as below. There are real time processes and non real time processes. Non real time processes can have nice values ...
11
votes
2answers
450 views

What are the effects, if any, of scheduler priorities and policies for threads in an uncontended cpuset?

I have a Linux system where we have used cgroups to create two cpu_exclusive cpusets, A and B, and where we have migrated all user threads and all unbound kernel threads to a cgroup attached to cpuset ...
10
votes
1answer
316 views

What does a computer actually do with its spare CPU cycles?

When a computer is not running at full load, in the context of Linux, what does it actually do? Between scheduled threads, if there is nothing to do, does it spin wait? Does it enter some sleep state? ...
9
votes
1answer
1k views

Why can a system become unresponsive?

I just executed dot (a program for drawing directed graphs) with an input file that was so big that it couldn't be rendered in a reasonable amount of time. My whole system froze. I could barely make ...
9
votes
1answer
223 views

Cronjob to Run and then Terminate

I want to add a cron entry that does something like: 00 00 * * * * /tmp/script.sh Is there something I can add to the end of the line, so that when it is finished, it will remove the line out of my ...
9
votes
1answer
3k views

How can you schedule a computer to boot at a specific time?

Usually BIOSes have an option to schedule a time to which to boot at. Is there a Unix/Linux interface to specify the scheduled boot?
9
votes
2answers
2k views

Does Linux kernel 3.x use the CFS process scheduler?

Does the latest version of the Linux kernel (3.x) still use the Completely Fair Scheduler (CFS) for process scheduling which was introduced in 2.6.x ? If it doesn't, which one does it use, and how ...
9
votes
1answer
5k views

Isolating cause of higher CPU usage on RHEL 6 vs RHEL 5

I'm currently looking to move our system from RHEL 5 to RHEL 6, but I've run into a snag with unexpectedly high CPU usage on the RHEL 6 machines. It appears that this may be due at least in some part ...
8
votes
3answers
825 views

how to queue a command to run after another command finishes?

Sometimes I start a program that takes a very long time to finish (emerge), then realize that I should go to bed instead of waiting for it. If I know this in the first place I would run program; halt ...
8
votes
2answers
30k views

What does “INFO: task XXX blocked for more than 120 seconds” exactly mean on Linux?

I had this message in my kernel log : INFO: task XXX blocked for more than 120 seconds. I would like to know what it means technically: under what conditions does the kernel display this message about ...
8
votes
5answers
8k views

Is there a workaround for a lack of scheduler in qbittorrent?

Unlike many other torrent clients, qbittorrent comes without a scheduling tool. Ideally, one can throttle downloads over a certain time of the day, on given days. Is there a workaround for this? Is ...
8
votes
3answers
7k views

Which Scheduling algorithm is used in Linux?

Recently in an interview I was asked about the Scheduling algorithm used by Linux Operating system. What is the algorithm used any why? Also, what algorithm is used in in real-time operating systems ...
8
votes
2answers
5k views

How can you determine which process scheduler is being used? [duplicate]

I.e. is it the O(1) scheduler, the CFS scheduler, or an older one?
7
votes
6answers
2k views

Can you make a linux system halt and boot my Raspberry-pi at certain times?

How to make a system turn itself off and back on at different times. For example I would have my "server" turn off at 4 A.M then turn back on at 5 A.M every day. Is this possible? I am using a ...
7
votes
3answers
3k views

Simple queuing system?

Given a commodity PC, we would like to use it to execute some tasks in the background round the clock. Basically, we would like to have commands like: add-task *insert command here* list-tasks ...
7
votes
1answer
274 views

Prioritise X applications with focus

Is there a way to prioritise X applications with focus, preferably both in terms of CPU and I/O? Something like all X applications are niced and ioniced down in priority, but when they gain focus ...
6
votes
4answers
465 views

Scheduling commands by system inactivity

So cron or at can schedule our commands to run at the exact time we need them to, but can we schedule commands to run when systems are inactive? Something like: echo "some_commands" | when 'cpu <...
6
votes
2answers
193 views

Why are there so few “running” processes?

On all of BSD/Linux/MacOS and Solaris, I made an observation - no matter how busy the system is, top always reports very few (usually 1-2) running processes. According to my limited understanding, a ...
6
votes
1answer
749 views

Why mkfifo behaves like a LIFO?

If i do. mkfifo /tmp/a echo 'one'>/tmp/a in the while from another terminal echo 'two'>/tmp/a and from a third terminal more /tmp/a Why i obtain as output of the last command this? ...
6
votes
1answer
2k views

How is cron scheduling actually implemented and makes sure scripts run on time?

I want to ask about cron jobs. OK, we place the scripts in the crontab and the cron daemon executes them. Now if I understand this, each minute, cron checks the crontab of each user and executes the ...
5
votes
2answers
3k views

How preemption works on Linux when a program has a timer less then 4ms?

Jiffies in most Linux system are defaulted to 250 (4ms). The questions is that what happens when a program has a usleep() less then 4ms ? Of course it works as should when it is scheduled. But what ...
5
votes
3answers
246 views

How can I verify `nice` is working?

Looking at different jobs running on a system with shared resources, it seems the nice values are being ignored. Many jobs with nice set at 19 are running at 100% cpu load while other many other jobs ...
5
votes
1answer
2k views

controlling priority of applications using cgroups

I would like to understand cgroups better and would like to understand the use-cases for applying cgroups. Are cgroups a good way for prioritizing different applications (i.e, giving higher priority ...
5
votes
1answer
200 views

Is the Unix process scheduler itself a process?

Is the Unix process scheduler itself a process, or does it piggyback on other processes in the same way a system call does (running kernel code in the user process with the kernel bit set)?
5
votes
1answer
579 views

Linux process scheduling - Cap/Weight based?

I am just trying to understand the basics of Linux scheduler. Is Linux scheduler a Cap based or weight based scheduler? I was previously using Xen. Now I am moving from Xen to KVM. I read VMs are ...
5
votes
1answer
42 views

Does linux stops processing related to GUI when we remove the desktop screen from connection from cabinet(CPU box)?

When there is big non interactive software running and if I required more processing power then, after removing the desktop screen does kernel stops processing related to GUI(graphical user interface) ...
4
votes
2answers
1k views

Schedule job at irregular intervals

It's simple enough to use cron to schedule a job to occur periodically. I'd like to have something occur less regularly -- say, run the job, then wait 2 to 12 hours before trying again. (Any ...
4
votes
2answers
868 views

How do I execute a script later?

I need to compile gcc45 on my computer and that's a lengthy and resource-intensive process for my computer, so I'd prefer to have it do it while I sleep (at night). What's the closest thing to: $ @...
4
votes
3answers
620 views

GNU: Delayed jobs Queue

Is there a simple way for me to add a shell command to a list of jobs to have run on the system when I'm not logged in? For example: I SSH into my system, decide that I want to read an ebook later, ...
4
votes
2answers
2k views

Run script every 30 min with systemd

I would like to execute a script every 30 min after booting into the system. I know you can use cron, but I don't plan to use this feature often therefore I'd like to try it with systemd. So far I ...
4
votes
2answers
803 views

How is the real-time priority of a process set by default?

I understand that, for scheduling purposes, Linux processes have a "nice" value and a real-time priority value and that these can be explicitly altered with the nice and chrt commands. If the user ...
4
votes
2answers
4k views

How to install and use at job scheduling?

I am not clear on the following: Is the process for at available to all linux installations? Or do would I need to do something to "install" it?
4
votes
4answers
1k views

How to prevent atd from running past jobs?

The at daemon is a great tool! However, if a job is scheduled for 8:00 am and the machine is off at that time, at will run the job whenever the machine is booted. What I would like to do is stop it ...
4
votes
2answers
159 views

Run program x minutes after finishing

My question is kinda related to a cron job I think, but I'm not entirely sure. Say I have a script (/home/me/myscript.sh) that does something, that can take an indeterminate amount of time to finish, ...
4
votes
1answer
71 views

Why is nice-level ignored? (Between different login sessions — honoured if started from same session.)

When I start two CPU-eating processes with different nice-level, e.g. Process 1: nice -19 sh -c 'while true; do :; done' Process 2: sh -c 'while :; do true; done' (I changed the order of : and ...
4
votes
1answer
540 views

Is it possible in taskwarrior for reminders about recurring tasks to expire automatically?

I'm using taskwarrior. I want to be reminded of something every week, but have that reminder go away automatically if I haven't completed it by the time the next week comes up. (Or, actually, I want ...
4
votes
3answers
1k views

How to monitor or kill a process which has been started by cron?

I have some bots, which are run by the System scheduler at given time interval. But sometimes due to some logical error I have to stop these bots manually. How can I find these processes run by the ...
4
votes
2answers
596 views

Are there any Workload Management subsystems for Linux?

Asked this on superuser, got no response: Can anyone tell me of the status/state of WLM (Workload Management) kernel scheduler systems in Linux? Alternatively, any user-space process goal-based load ...
4
votes
2answers
2k views

chrt(): “failed to set pid XXX's policy” on one machine, but not others

I have several Linux machines, all of them running the same kernel (Ubuntu 12.04, 3.5.0-45-generic). On one of them, I am unable to use chrt at all. If I attempt to use it on a new process, I get the ...
4
votes
1answer
1k views

Using sched_rt_period_us for setting maximum time between task calls of order of 10ms

I realize sched_rt_period_us and sched_rt_runtime_us are meant to prevent freezing the system in case of runaway RT task. I wonder though, if it's possible to use a small value of sched_rt_period_us ...
3
votes
2answers
494 views

How does a script/program executes in unix?

I have a doubt about the execution pattern of a unix script. For example a script containing lines: command B function C() { Myscript // Myscript is a script command D } command E and ...