# Server attributes **URL:** \ **Category:** Users/Site Administrators\ **Created:** [January 14, 2026, 5:54am UTC](https://community.openpbs.org/t/server-attributes/4209 "2026-01-14T05:54:29Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![wakaka](https://avatars.discourse-cdn.com/v4/letter/w/d07c76/32.png) [@wakaka](https://community.openpbs.org/u/wakaka)\ **Post date:** [January 14, 2026, 5:54am UTC](https://community.openpbs.org/t/server-attributes/4209/1 "2026-01-14T05:54:29Z")
How do I understand these two attributes? ```auto sched_cycle_length = 00:20:00 scheduler_iteration = 600 ``` ---
**Author:** ![adarsh](https://avatars.discourse-cdn.com/v4/letter/a/f07891/32.png) [@adarsh](https://community.openpbs.org/u/adarsh)\ **Post date:** [January 14, 2026, 7:44am UTC](https://community.openpbs.org/t/server-attributes/4209/2 "2026-01-14T07:44:20Z")
Reference: [https://2026.help.altair.com/2026.0/PBS%20Professional/PBS2026.0.pdf](https://2026.help.altair.com/2026.0/PBS%20Professional/PBS2026.0.pdf) **scheduler\_iteration** and **sched\_cycle\_length** are both scheduler attributes that manage the timing of scheduling cycles, but they control different aspects of the process. **scheduler\_iteration (Frequency)**: : attribute defines the **time interval between the start of scheduling cycles** : It acts as a timer to ensure the scheduler periodically checks the queue for jobs that can be run, even if the server hasn’t been triggered by new submissions or job completions **sched\_cycle\_length (Maximum Duration)**: The **sched\_cycle\_length** attribute sets a **limit on how long a single scheduling cycle is allowed to run**. It is a safety mechanism that instructs the scheduler to **terminate its current cycle** if the work (examining and running jobs) exceeds this specified duration **sched\_cycle\_length :** one-day bus pass **scheduler\_iteration:** the number of bus journeys you have taken during that day , each journey is like trying to scheduled jobs.[Scheduler iterations happen within the scheduling cycle] **example1:** [Scheduler Cycle Starts] scheduler\_iteration 1 scheduler\_iteration2 scheduler\_iteration 3 [Scheduler Cycle Ends] \<─── sched\_cycle\_length ───\> [Next Scheduler Cycle Starts] scheduler\_iteration 1 scheduler\_iteration 2 [Scheduler Cycle Ends] example 2: If you check your scheduler logs: 01/13/2026 20:35:47;0080;pbs\_sched;Req;;Starting Scheduling Cycle 01/13/2026 20:35:47;0080;pbs\_sched;Job;5104.pbsserver;Considering job to run 01/13/2026 20:35:47;0040;pbs\_sched;Job;5104.pbsserver;Job run 01/13/2026 20:35:47;0080;pbs\_sched;Job;5105.insightpro;Considering job to run 01/13/2026 20:35:47;0040;pbs\_sched;Job;5105.pbsserver;Job run 01/13/2026 20:35:47;0080;pbs\_sched;Job;5106.pbsserver;Considering job to run 01/13/2026 20:35:47;0040;pbs\_sched;Job;5106.pbsserver;Job run 01/13/2026 20:35:47;0080;pbs\_sched;Job;5107.pbsserver;Considering job to run 01/13/2026 20:35:47;0040;pbs\_sched;Job;5107.pbsserver;Job run 01/13/2026 20:35:47;0080;pbs\_sched;Req;;Leaving Scheduling Cycle . . 01/13/2026 20:35:47;0080;pbs\_sched;Req;;Starting Scheduling Cycle 01/13/2026 20:35:47;0080;pbs\_sched;Req;;Leaving Scheduling Cycle 20:35:47 [Cycle starts] 20:35:47 [Cycle ends immediately] (waiting up to 20 minutes = sched\_cycle\_length) ~20:55:47 [Next cycle allowed] ---
**Author:** ![wakaka](https://avatars.discourse-cdn.com/v4/letter/w/d07c76/32.png) [@wakaka](https://community.openpbs.org/u/wakaka)\ **Post date:** [January 16, 2026, 2:47am UTC](https://community.openpbs.org/t/server-attributes/4209/3 "2026-01-16T02:47:44Z")
I’m still confused: The default value for `sched_cycle_length` is 20 minutes, and the default value for `scheduler_iteration` is 600 seconds. Submitting a job immediately triggers scheduling, starting a scheduling cycle. The maximum runtime of this cycle is limited by the `sched_cycle_length` attribute. After this time, the scheduling cycle ends. If any jobs are not yet scheduled, they wait for the time set by the `scheduler_iteration` attribute before being processed in the next scheduling cycle, it waits 600 seconds. However, I continuously submit a large number of jobs. Some jobs start executing, while others are queued due to insufficient resources. But subsequently, as long as resources are sufficient, some jobs in Q state are immediately scheduled for execution, and other jobs are constantly being submitted and queued. I don’t perceive any waiting time associated with these two attributes. Why is this? I never feel the need to wait 20 minutes + 600 seconds for a job to be scheduled for execution. Whether a job executes depends solely on resource availability. ---
**Author:** ![adarsh](https://avatars.discourse-cdn.com/v4/letter/a/f07891/32.png) [@adarsh](https://community.openpbs.org/u/adarsh)\ **Post date:** [January 16, 2026, 6:31am UTC](https://community.openpbs.org/t/server-attributes/4209/4 "2026-01-16T06:31:52Z")
The PBS scheduler is event driven and not purely time driven. You can think sched\_cycle\_length as the wall clock of one scheduling cycle (example of one day bus pass).. It is can thought of a safety mechanism , you can hit the large schedu\_cycle\_length say when there are are lot of server\_dyn\_res scripts, million of jobs , too many policies . Referece: [https://2026.help.altair.com/2026.0/PBS%20Professional/PBS2026.0.pdf](https://2026.help.altair.com/2026.0/PBS%20Professional/PBS2026.0.pdf) ![image](https://canada1.discourse-cdn.com/flex030/uploads/pbspro/original/1X/de9e6b5b64cf9a27f4369573475d6ddce7645279.png) If there is no such event trigger on the PBS Server, you can manually triggerscheduling cycle by running qmgr -c “set server scheduing = true” or it will trigger based on the scheduler iteration interval. ![image](https://canada1.discourse-cdn.com/flex030/uploads/pbspro/original/1X/03213914c3fe4e75c8e24821b23164ca3b249928.png) ---
**Author:** ![sarah](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@sarah](https://community.openpbs.org/u/sarah)\ **Post date:** [January 21, 2026, 2:52pm UTC](https://community.openpbs.org/t/server-attributes/4209/5 "2026-01-21T14:52:01Z")
You should see this with OpenPBS because sched\_cycle\_length and scheduler\_iteration are just higher limits, not forced delays. The planner tries to run any job that has resources right away, so jobs that are waiting in line can start right away. The 20min and 600s only matter if the dispatcher is idle or has reached its cycle limit. When resources are available, jobs are not slowed down. Think of them more as safety timers than as times to wait.