Solved: [error] Unable to obtain semaphore.
Today we will see an interesting article how to resolve below error.
I. Error Details
[root@ngelinux001 conf.d]# service httpd start
Starting httpd: [Wed May 18 23:41:31 2022] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Wed May 18 23:41:31 2022] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Wed May 18 23:41:31 2022] [error] Server certificate is expired: 'Server-Cert'
[Wed May 18 23:41:31 2022] [error] Server certificate is expired: 'Server-Cert'
[Wed May 18 23:41:31 2022] [error] Unable to obtain semaphore.
[Wed May 18 23:41:31 2022] [error] Unable to obtain semaphore.
[FAILED]
II. Solution
a. First check the semaphores allocated.
[root@ngelinux001 conf.d]# ipcs -u semaphores ------ Shared Memory Status -------- segments allocated 6 pages allocated 299 pages resident 296 pages swapped 2 Swap performance: 0 attempts 0 successes ------ Semaphore Status -------- used arrays = 127 allocated semaphores = 127 ------ Messages: Status -------- allocated queues = 0 used headers = 0 used space = 0 bytes [root@ngelinux001 conf.d]#
b. Checkout the shmid allocated.
[root@ngelinux001 conf.d]# ipcs -p ------ Shared Memory Creator/Last-op -------- shmid owner cpid lpid 163840 postgres 10279 22208 84475905 root 28693 28693 262146 eldar 12487 30110 29622275 pvsqa 27022 17242 29655044 pvsqa 27022 27022 71958533 pvsqa 27273 19058 ------ Message Queues PIDs -------- msqid owner lspid lrpid [root@ngelinux001 conf.d]#
c. Check semids and clear them.
[root@ngelinux001 conf.d]# ipcs -s ------ Semaphore Arrays -------- key semid owner perms nsems 0x00000000 0 root 600 1 0x00000000 32769 root 600 1 0x00000000 5799939 apache 600 1 0x00000000 163844 apache 600 1 0x00000000 196613 apache 600 1 0x00000000 229382 apache 600 1 0x00000000 262151 apache 600 1 0x00000000 294920 apache 600 1 0x00000000 393225 apache 600 1 0x00000000 425994 apache 600 1 0x00000000 458763 apache 600 1 0x00000000 491532 apache 600 1 0x00000000 524301 apache 600 1 0x00000000 622606 apache 600 1 0x00000000 655375 apache 600 1 0x00000000 688144 apache 600 1 0x00000000 720913 apache 600 1 0x00000000 753682 apache 600 1 0x00000000 851987 apache 600 1 0x00000000 884756 apache 600 1 0x00000000 917525 apache 600 1 0x00000000 950294 apache 600 1 0x00000000 983063 apache 600 1 0x00000000 1081368 apache 600 1 0x00000000 1114137 apache 600 1 0x00000000 1146906 apache 600 1 0x00000000 1179675 apache 600 1 0x00000000 1212444 apache 600 1 0x00004155 1245213 pvsqa 666 1 0x00000000 1343518 apache 600 1 0x00000000 1376287 apache 600 1 0x00000000 1409056 apache 600 1 0x00000000 1441825 apache 600 1 0x00000000 1474594 apache 600 1 0x00000000 1572899 apache 600 1 0x00000000 1605668 apache 600 1 0x00000000 1638437 apache 600 1 0x00000000 1671206 apache 600 1 0x00000000 1703975 apache 600 1 0x00000000 1802280 apache 600 1 0x00000000 1835049 apache 600 1 0x00000000 1867818 apache 600 1 0x00000000 1900587 apache 600 1 0x00000000 1933356 apache 600 1 0x00000000 2031661 apache 600 1 0x00000000 2064430 apache 600 1 0x00000000 2097199 apache 600 1 0x00000000 2129968 apache 600 1 0x00000000 2162737 apache 600 1 0x00000000 2261042 apache 600 1 0x00000000 2293811 apache 600 1 0x00000000 2326580 apache 600 1 0x00000000 2359349 apache 600 1 0x00000000 2392118 apache 600 1 0x00000000 2490423 apache 600 1 0x00000000 2523192 apache 600 1 0x00000000 2555961 apache 600 1 0x00000000 2588730 apache 600 1 0x00000000 2621499 apache 600 1 0x00000000 2719804 apache 600 1 0x00000000 2752573 apache 600 1 0x00000000 2785342 apache 600 1 0x00000000 2818111 apache 600 1 0x00000000 2850880 apache 600 1 0x00000000 2949185 apache 600 1 0x00000000 2981954 apache 600 1 0x00000000 3014723 apache 600 1 0x00000000 3047492 apache 600 1 0x00000000 3080261 apache 600 1 0x00000000 3178566 apache 600 1 0x00000000 3211335 apache 600 1 0x00000000 3244104 apache 600 1 0x00000000 3276873 apache 600 1 0x00000000 3309642 apache 600 1 0x00000000 3407947 apache 600 1 0x00000000 3440716 apache 600 1 0x00000000 3473485 apache 600 1 0x00000000 3506254 apache 600 1 0x00000000 3539023 apache 600 1 0x00000000 3637328 apache 600 1 0x00000000 3670097 apache 600 1 0x00000000 3702866 apache 600 1 0x00000000 3735635 apache 600 1 0x00000000 3768404 apache 600 1 0x00000000 3866709 apache 600 1 0x00000000 3899478 apache 600 1 0x00000000 3932247 apache 600 1 0x00000000 3965016 apache 600 1 0x00000000 3997785 apache 600 1 0x00000000 4096090 apache 600 1 0x00000000 4128859 apache 600 1 0x00000000 4161628 apache 600 1 0x00000000 4194397 apache 600 1 0x00000000 4227166 apache 600 1 0x00000000 4325471 apache 600 1 0x00000000 4358240 apache 600 1 0x00000000 4391009 apache 600 1 0x00000000 4423778 apache 600 1 0x00000000 4456547 apache 600 1 0x00000000 4554852 apache 600 1 0x00000000 4587621 apache 600 1 0x00000000 4620390 apache 600 1 0x00000000 4653159 apache 600 1 0x00000000 4685928 apache 600 1 0x00000000 4784233 apache 600 1 0x00000000 4817002 apache 600 1 0x00000000 4849771 apache 600 1 0x00000000 4882540 apache 600 1 0x00000000 4915309 apache 600 1 0x00000000 5013614 apache 600 1 0x00000000 5046383 apache 600 1 0x00000000 5079152 apache 600 1 0x00000000 5111921 apache 600 1 0x00000000 5144690 apache 600 1 0x00000000 5242995 apache 600 1 0x00000000 5275764 apache 600 1 0x00000000 5308533 apache 600 1 0x00000000 5341302 apache 600 1 0x00000000 5374071 apache 600 1 0x00000000 5472376 apache 600 1 0x00000000 5505145 apache 600 1 0x00000000 5537914 apache 600 1 0x00000000 5570683 apache 600 1 0x00000000 5603452 apache 600 1 0x00000000 5832829 apache 600 1 0x00000000 5865598 apache 600 1 0x00000000 5898367 apache 600 1 [root@ngelinux001 conf.d]#
d. Get PID of the semid
[root@ngelinux001 conf.d]# ipcs -s -i 5898367 Semaphore Array semid=5898367 uid=48 gid=48 cuid=0 cgid=0 mode=0600, access_perms=0600 nsems = 1 otime = Not set ctime = Wed May 18 03:00:48 2022 semnum value ncount zcount pid 0 1 0 0 28693
e. Remove this semaphore
[root@ngelinux001 conf.d]# ipcrm -m 5898367 ipcrm: invalid id (5898367)
f. Remove all semaphores
[root@ngelinux001 conf.d]# for i in `ipcs -s | grep -i apache | awk '{print $2}'`; do ipcrm -m $i; done
ipcrm: already removed id (5799939)
ipcrm: already removed id (163844)
ipcrm: already removed id (196613)
ipcrm: invalid id (229382)
ipcrm: invalid id (262151)
ipcrm: invalid id (294920)
ipcrm: invalid id (393225)
ipcrm: invalid id (425994)
ipcrm: invalid id (458763)
ipcrm: invalid id (491532)
ipcrm: invalid id (524301)
ipcrm: invalid id (622606)
ipcrm: invalid id (655375)
ipcrm: invalid id (688144)
ipcrm: invalid id (720913)
ipcrm: invalid id (753682)
III. Permanent Fix: Increase the semaphore limit on server.
### Enter below two variables in sysctl.conf file. # cat /etc/sysctl.conf kernel.msgmni = 512 kernel.sem = 250 128000 32 512 ### Print the new values. # sysctl -p
IV. Restart the http service now and the error will be removed.
[root@ngelinux001 kernel]# service httpd restart
Stopping httpd: [ OK ]
Starting httpd: [Thu May 19 00:10:41 2022] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Thu May 19 00:10:41 2022] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[OK]
[root@ngelinux001 kernel]#