https://bz.apache.org/bugzilla/show_bug.cgi?id=62044
Bug ID: 62044
Summary: shared memory segments are not found in global list,
but appear to exist in kernel.
Product: Apache httpd-2
Version: 2.4.29
Hardware: PC
OS: Linux
Status: NEW
Severity: critical
Priority: P2
Component: mod_proxy_balancer
Assignee: bugs@httpd.apache.org
Reporter: m...@blackmans.org
Target Milestone: ---
With a large number of vhosts ( > 1000 ) and proxy balancer configurations ( >
1000), we are seeing Apache exit at start up time with a configuration error
(very frequently) with an error like.
[Wed Jan 10 16:28:45.853599 2018] [slotmem_shm:error] [pid 29764:tid
140038537377536] (17)File exists: AH02611: create:
apr_shm_create(/apache24/logs/slotmem-shm-p71143bd8_balancer1.shm) failed
[Wed Jan 10 16:28:45.853641 2018] [:emerg] [pid 29764:tid 140038537377536]
AH00020: Configuration Failed, exiting
turning on trace5 level logs we see things like the following for a single
balancer worker (I filtered on the balance SHM name)
[Thu Jan 25 03:48:08.397926 2018] [slotmem_shm:debug] [pid 13310:tid
140455729428224] mod_slotmem_shm.c(364): AH02602: create didn't find
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm in global list
[Thu Jan 25 03:48:08.397932 2018] [slotmem_shm:debug] [pid 13310:tid
140455729428224] mod_slotmem_shm.c(374): AH02300: create
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm: 1176/2
[Thu Jan 25 03:48:08.398076 2018] [slotmem_shm:debug] [pid 13310:tid
140455729428224] mod_slotmem_shm.c(417): AH02611: create:
apr_shm_create(/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm) succeeded
[Thu Jan 25 03:48:58.529349 2018] [slotmem_shm:debug] [pid 45813:tid
139795075143424] mod_slotmem_shm.c(364): AH02602: create didn't find
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm in global list
[Thu Jan 25 03:48:58.529357 2018] [slotmem_shm:debug] [pid 45813:tid
139795075143424] mod_slotmem_shm.c(374): AH02300: create
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm: 1176/2
[Thu Jan 25 03:49:01.835207 2018] [slotmem_shm:debug] [pid 46229:tid
139795075143424] mod_slotmem_shm.c(496): AH02301: attach looking for
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm
[Thu Jan 25 03:49:01.835222 2018] [slotmem_shm:debug] [pid 46625:tid
139795075143424] mod_slotmem_shm.c(496): AH02301: attach looking for
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm
[Thu Jan 25 03:49:01.835230 2018] [slotmem_shm:debug] [pid 46229:tid
139795075143424] mod_slotmem_shm.c(509): AH02302: attach found
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm: 1176/2
[Thu Jan 25 03:49:01.835254 2018] [slotmem_shm:debug] [pid 46625:tid
139795075143424] mod_slotmem_shm.c(509): AH02302: attach found
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm: 1176/2
[Thu Jan 25 03:49:01.886171 2018] [slotmem_shm:debug] [pid 47011:tid
139795075143424] mod_slotmem_shm.c(496): AH02301: attach looking for
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm
[Thu Jan 25 03:49:01.886284 2018] [slotmem_shm:debug] [pid 47011:tid
139795075143424] mod_slotmem_shm.c(509): AH02302: attach found
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm: 1176/2
[Thu Jan 25 03:49:01.899288 2018] [slotmem_shm:debug] [pid 47281:tid
139795075143424] mod_slotmem_shm.c(496): AH02301: attach looking for
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm
[Thu Jan 25 03:49:01.899321 2018] [slotmem_shm:debug] [pid 47281:tid
139795075143424] mod_slotmem_shm.c(509): AH02302: attach found
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm: 1176/2
[Thu Jan 25 03:53:03.516455 2018] [slotmem_shm:debug] [pid 45813:tid
139795075143424] mod_slotmem_shm.c(364): AH02602: create didn't find
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm in global list
[Thu Jan 25 03:53:03.516462 2018] [slotmem_shm:debug] [pid 45813:tid
139795075143424] mod_slotmem_shm.c(374): AH02300: create
/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm: 1176/2
[Thu Jan 25 03:53:03.516499 2018] [slotmem_shm:error] [pid 45813:tid
139795075143424] (17)File exists: AH02611: create:
apr_shm_create(/apache24/logs/slotmem-shm-pe1b232bb_balancer1.shm) failed
In other words, in the space of five minutes, the balancer was not found in the
global list (03:48:08), successfully created, then found several times, then
went missing at 03:53:03, and then failed to create it, which then triggered an
Apache exit (not shown here)
Rather confusingly, the choice of the DefaultRuntimeDirectory has an impact on
frequence.
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