Is there a downside to using flock in cron jobs?
I use several cron jobs, where they run frequently I use flock to prevent duplicate jobs running. I just thought that it seems to make sense to use flock on every job, irrespective of the frequency, but is there any downside to doing that?
I am 100% Linux with Mint, Raspbian and Ubuntu server.
linux cron
edited Jan 8 at 19:52
JakeGould
31.2k1096138
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
add a comment |
I use several cron jobs, where they run frequently I use flock to prevent duplicate jobs running. I just thought that it seems to make sense to use flock on every job, irrespective of the frequency, but is there any downside to doing that?
I am 100% Linux with Mint, Raspbian and Ubuntu server.
linux cron
edited Jan 8 at 19:52
JakeGould
31.2k1096138
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
Please do not crosspost. See Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
– DavidPostill♦
Jan 8 at 20:06
add a comment |
I use several cron jobs, where they run frequently I use flock to prevent duplicate jobs running. I just thought that it seems to make sense to use flock on every job, irrespective of the frequency, but is there any downside to doing that?
I am 100% Linux with Mint, Raspbian and Ubuntu server.
linux cron
edited Jan 8 at 19:52
JakeGould
31.2k1096138
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
I use several cron jobs, where they run frequently I use flock to prevent duplicate jobs running. I just thought that it seems to make sense to use flock on every job, irrespective of the frequency, but is there any downside to doing that?
I am 100% Linux with Mint, Raspbian and Ubuntu server.
linux cron
linux cron
edited Jan 8 at 19:52
JakeGould
31.2k1096138
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
edited Jan 8 at 19:52
JakeGould
31.2k1096138
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
edited Jan 8 at 19:52
JakeGould
31.2k1096138
edited Jan 8 at 19:52
JakeGould
31.2k1096138
edited Jan 8 at 19:52
JakeGould
31.2k1096138
31.2k1096138
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
asked Jan 8 at 19:11
Mick SulleyMick Sulley
31
31
Please do not crosspost. See Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
– DavidPostill♦
Jan 8 at 20:06
add a comment |
Please do not crosspost. See Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
– DavidPostill♦
Jan 8 at 20:06
Please do not crosspost. See Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
– DavidPostill♦
Jan 8 at 20:06
Please do not crosspost. See Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
– DavidPostill♦
Jan 8 at 20:06
add a comment |
1 Answer
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The only consistent downside is that there's extra overhead to using flock. Aside from the obvious aspect of having to open a file and lock it, you also have the fact that there's going to be another process involved (or at least an extra executable and call to exec() if you're using the --no-fork option), and there's some extra overhead in the cleanup (because the OS has to release the lock when it automatically closes the file).
There are also a couple of other really situationally specific downsides to locking cron jobs like this (this is not an exhaustive list):
- If you need exclusive locks, you need a writable filesystem path, otherwise the
flockcommand will always fail. This means that:
- If you're not careful, a filesystem error can completely stop your cron jobs from running (if it causes the path you use for locks to get remounted read-only).
- On some tightly secured devices, you may have to give some extra permissions to the cron jobs so that they can run.
- In some cases, you actually want the new instance of the cron job to be the one that continues, not the old one. The best example I can give for this is a high-frequency cron job that runs every few minutes to synchronize files to another system, where waiting until the previous instance is finished may delay the most recent updates by an arbitrarily long time. If, instead, you have the cron job kill any old copies of itself when it starts, you can still progress, and recent changes are more likely to get propagated out quickly.
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
add a comment |
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1 Answer
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The only consistent downside is that there's extra overhead to using flock. Aside from the obvious aspect of having to open a file and lock it, you also have the fact that there's going to be another process involved (or at least an extra executable and call to exec() if you're using the --no-fork option), and there's some extra overhead in the cleanup (because the OS has to release the lock when it automatically closes the file).
There are also a couple of other really situationally specific downsides to locking cron jobs like this (this is not an exhaustive list):
- If you need exclusive locks, you need a writable filesystem path, otherwise the
flockcommand will always fail. This means that:
- If you're not careful, a filesystem error can completely stop your cron jobs from running (if it causes the path you use for locks to get remounted read-only).
- On some tightly secured devices, you may have to give some extra permissions to the cron jobs so that they can run.
- In some cases, you actually want the new instance of the cron job to be the one that continues, not the old one. The best example I can give for this is a high-frequency cron job that runs every few minutes to synchronize files to another system, where waiting until the previous instance is finished may delay the most recent updates by an arbitrarily long time. If, instead, you have the cron job kill any old copies of itself when it starts, you can still progress, and recent changes are more likely to get propagated out quickly.
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
add a comment |
The only consistent downside is that there's extra overhead to using flock. Aside from the obvious aspect of having to open a file and lock it, you also have the fact that there's going to be another process involved (or at least an extra executable and call to exec() if you're using the --no-fork option), and there's some extra overhead in the cleanup (because the OS has to release the lock when it automatically closes the file).
There are also a couple of other really situationally specific downsides to locking cron jobs like this (this is not an exhaustive list):
- If you need exclusive locks, you need a writable filesystem path, otherwise the
flockcommand will always fail. This means that:
- If you're not careful, a filesystem error can completely stop your cron jobs from running (if it causes the path you use for locks to get remounted read-only).
- On some tightly secured devices, you may have to give some extra permissions to the cron jobs so that they can run.
- In some cases, you actually want the new instance of the cron job to be the one that continues, not the old one. The best example I can give for this is a high-frequency cron job that runs every few minutes to synchronize files to another system, where waiting until the previous instance is finished may delay the most recent updates by an arbitrarily long time. If, instead, you have the cron job kill any old copies of itself when it starts, you can still progress, and recent changes are more likely to get propagated out quickly.
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
add a comment |
The only consistent downside is that there's extra overhead to using flock. Aside from the obvious aspect of having to open a file and lock it, you also have the fact that there's going to be another process involved (or at least an extra executable and call to exec() if you're using the --no-fork option), and there's some extra overhead in the cleanup (because the OS has to release the lock when it automatically closes the file).
There are also a couple of other really situationally specific downsides to locking cron jobs like this (this is not an exhaustive list):
- If you need exclusive locks, you need a writable filesystem path, otherwise the
flockcommand will always fail. This means that:
- If you're not careful, a filesystem error can completely stop your cron jobs from running (if it causes the path you use for locks to get remounted read-only).
- On some tightly secured devices, you may have to give some extra permissions to the cron jobs so that they can run.
- In some cases, you actually want the new instance of the cron job to be the one that continues, not the old one. The best example I can give for this is a high-frequency cron job that runs every few minutes to synchronize files to another system, where waiting until the previous instance is finished may delay the most recent updates by an arbitrarily long time. If, instead, you have the cron job kill any old copies of itself when it starts, you can still progress, and recent changes are more likely to get propagated out quickly.
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
The only consistent downside is that there's extra overhead to using flock. Aside from the obvious aspect of having to open a file and lock it, you also have the fact that there's going to be another process involved (or at least an extra executable and call to exec() if you're using the --no-fork option), and there's some extra overhead in the cleanup (because the OS has to release the lock when it automatically closes the file).
There are also a couple of other really situationally specific downsides to locking cron jobs like this (this is not an exhaustive list):
- If you need exclusive locks, you need a writable filesystem path, otherwise the
flockcommand will always fail. This means that:
- If you're not careful, a filesystem error can completely stop your cron jobs from running (if it causes the path you use for locks to get remounted read-only).
- On some tightly secured devices, you may have to give some extra permissions to the cron jobs so that they can run.
- In some cases, you actually want the new instance of the cron job to be the one that continues, not the old one. The best example I can give for this is a high-frequency cron job that runs every few minutes to synchronize files to another system, where waiting until the previous instance is finished may delay the most recent updates by an arbitrarily long time. If, instead, you have the cron job kill any old copies of itself when it starts, you can still progress, and recent changes are more likely to get propagated out quickly.
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
answered Jan 8 at 19:47
Austin HemmelgarnAustin Hemmelgarn
2,62419
2,62419
add a comment |
add a comment |
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Please do not crosspost. See Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?
– DavidPostill♦
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