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I have a web server running CentOS 7, on which the systemd process is using nearly 4 GB of RAM after a couple weeks of uptime. RAM usage is increasing steadily at about 200MB per day. This and related processes like systemd-logind and dbus-daemon also use a sizable chunk of CPU much of the time. My other CentOS 6 server using "init" instead of systemd has no such resource usage.

In the top example below, during normal web serving without other processes running, systemd, systemd-logind, systemd-journal, and dbus-daemon use a combined total 10.7% of a quad-core CPU, and systemd is consuming 19% of the system's 16GB of RAM. This is not normal behavior, and after searching around I haven't found anyone else with this issue. What could cause this resource hogging? Any suggestions would be appreciated.

Output from top during an idle period (except for web serving):

top - 08:51:31 up 16 days, 13:43,  2 users,  load average: 1.84, 1.39, 1.07
Tasks: 297 total,   2 running, 295 sleeping,   0 stopped,   0 zombie
%Cpu(s):  5.6 us,  3.6 sy,  0.0 ni, 90.6 id,  0.1 wa,  0.0 hi,  0.1 si,  0.0 st
KiB Mem : 16212992 total,  2466564 free,  4275764 used,  9470664 buff/cache
KiB Swap:  4194300 total,  4070740 free,   123560 used. 10707392 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                          
  743 dbus      20   0   27104   1856   1152 S   3.3  0.0 304:27.19 dbus-daemon                                      
    1 root      20   0 3247784 2.920g   1800 S   3.0 18.9 287:41.35 systemd                                          
  737 root      20   0   27416   2524   1304 S   2.7  0.0 225:32.66 systemd-logind                                   
  736 root      20   0  434760   3756   3076 S   2.0  0.0 172:26.53 NetworkManager                                   
  548 root      20   0   82276  34652  34516 S   1.7  0.2 160:20.16 systemd-journal                                  
  770 polkitd   20   0  522920   2956   2248 S   1.7  0.0 120:06.11 polkitd                                          
  716 root      16  -4  116744   1368   1312 S   1.3  0.0  93:26.54 auditd                                           
 3778 nginx     20   0  446488  14688   6564 S   1.3  0.1   2:18.80 php-fpm                                          
 3847 nginx     20   0  446316  14588   6548 S   1.3  0.1   2:19.29 php-fpm                                          
 7000 nginx     20   0  446132  14400   6544 S   1.3  0.1   1:22.77 php-fpm                                          
14862 nginx     20   0  446304  14600   6580 S   1.3  0.1   1:32.25 php-fpm                                          
30333 nginx     20   0  446292  14468   6528 S   1.3  0.1   1:40.78 php-fpm                                          
  740 root      20   0  784980  20112  19696 S   1.0  0.1  76:12.69 rsyslogd                                         
 3521 nginx     20   0  446188  14848   6748 S   1.0  0.1   2:20.00 php-fpm                                          
 3687 nginx     20   0  446036  14688   6764 S   1.0  0.1   2:20.45 php-fpm                                          
 3689 nginx     20   0  446408  14604   6552 S   1.0  0.1   2:19.75 php-fpm                                          
 3774 nginx     20   0  446288  14568   6552 S   1.0  0.1   2:19.68 php-fpm                                          
 3836 nginx     20   0  447416  15572   6564 S   1.0  0.1   2:21.06 php-fpm                                          
 4861 nginx     20   0  446260  14576   6540 S   1.0  0.1   2:18.94 php-fpm                                          
 4862 nginx     20   0  446508  15084   6764 S   1.0  0.1   2:20.71 php-fpm                                          
13538 nginx     20   0  447204  15452   6572 S   1.0  0.1   1:32.33 php-fpm                                          
15530 nginx     20   0  446292  14520   6528 S   1.0  0.1   1:32.55 php-fpm                                          
28468 nginx     20   0  446356  14672   6568 S   1.0  0.1   1:42.21 php-fpm                                          
29564 nginx     20   0  446292  14536   6548 S   1.0  0.1   1:41.11 php-fpm                                          
30851 nginx     20   0  445956  14568   6748 S   1.0  0.1   1:49.66 php-fpm 

Edit 2-14-16

I may have found something relevant in the output of "sudo journalctl" (see below). There are many lines occurring every second for hours at a time regarding SSH connections from one of my other production servers. These are rsync processes transferring files from the remote server to the server in question. This turns out to explain the CPU usage of systemd, systemd-logind, NetworkManager, and systemd-journal.

However, this could not explain the memory leak, which is the biggest problem. Since the original writing of this post a couple days ago, systemd has increased from 18.9% to 21.4% usage of system memory.

The log below has been modified to replace the real domain name and IP address of the servers.

Feb 14 10:02:13 hostname.domain.com systemd-logind[737]: New session 6467482 of user tropicg9.
Feb 14 10:02:13 hostname.domain.com systemd[1]: Started Session 6467482 of user tropicg9.
Feb 14 10:02:13 hostname.domain.com systemd[1]: Starting Session 6467482 of user tropicg9.
Feb 14 10:02:13 hostname.domain.com sshd[9665]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:13 hostname.domain.com sshd[9667]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:13 hostname.domain.com sshd[9665]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:13 hostname.domain.com systemd-logind[737]: Removed session 6467482.
Feb 14 10:02:14 hostname.domain.com sshd[9728]: Accepted publickey for tropicg9 from 1.2.3.4 port 45289 ssh2: RSA 0b:
Feb 14 10:02:14 hostname.domain.com systemd-logind[737]: New session 6467483 of user tropicg9.
Feb 14 10:02:14 hostname.domain.com systemd[1]: Started Session 6467483 of user tropicg9.
Feb 14 10:02:14 hostname.domain.com systemd[1]: Starting Session 6467483 of user tropicg9.
Feb 14 10:02:14 hostname.domain.com sshd[9728]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:14 hostname.domain.com sshd[9735]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:14 hostname.domain.com sshd[9728]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:14 hostname.domain.com systemd-logind[737]: Removed session 6467483.
Feb 14 10:02:15 hostname.domain.com sshd[9876]: Accepted publickey for tropicg9 from 1.2.3.4 port 45290 ssh2: RSA 0b:
Feb 14 10:02:15 hostname.domain.com systemd-logind[737]: New session 6467484 of user tropicg9.
Feb 14 10:02:15 hostname.domain.com systemd[1]: Started Session 6467484 of user tropicg9.
Feb 14 10:02:15 hostname.domain.com systemd[1]: Starting Session 6467484 of user tropicg9.
Feb 14 10:02:15 hostname.domain.com sshd[9876]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:15 hostname.domain.com sshd[9883]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:15 hostname.domain.com sshd[9876]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:15 hostname.domain.com systemd-logind[737]: Removed session 6467484.
Feb 14 10:02:20 hostname.domain.com sshd[10333]: Accepted publickey for tropicg9 from 1.2.3.4 port 45291 ssh2: RSA 0b
Feb 14 10:02:20 hostname.domain.com systemd-logind[737]: New session 6467485 of user tropicg9.
Feb 14 10:02:20 hostname.domain.com systemd[1]: Started Session 6467485 of user tropicg9.
Feb 14 10:02:20 hostname.domain.com systemd[1]: Starting Session 6467485 of user tropicg9.
Feb 14 10:02:20 hostname.domain.com sshd[10333]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:20 hostname.domain.com sshd[10342]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:20 hostname.domain.com sshd[10333]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:20 hostname.domain.com systemd-logind[737]: Removed session 6467485.
Feb 14 10:02:21 hostname.domain.com sshd[10450]: Accepted publickey for tropicg9 from 1.2.3.4 port 45292 ssh2: RSA 0b
Feb 14 10:02:21 hostname.domain.com systemd-logind[737]: New session 6467486 of user tropicg9.
Feb 14 10:02:21 hostname.domain.com systemd[1]: Started Session 6467486 of user tropicg9.
Feb 14 10:02:21 hostname.domain.com systemd[1]: Starting Session 6467486 of user tropicg9.
Feb 14 10:02:21 hostname.domain.com sshd[10450]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:21 hostname.domain.com sshd[10457]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:21 hostname.domain.com sshd[10450]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:21 hostname.domain.com systemd-logind[737]: Removed session 6467486.
Feb 14 10:02:22 hostname.domain.com sshd[10473]: Accepted publickey for tropicg9 from 1.2.3.4 port 45293 ssh2: RSA 0b
Feb 14 10:02:22 hostname.domain.com systemd-logind[737]: New session 6467487 of user tropicg9.
Feb 14 10:02:22 hostname.domain.com systemd[1]: Started Session 6467487 of user tropicg9.
Feb 14 10:02:22 hostname.domain.com systemd[1]: Starting Session 6467487 of user tropicg9.
Feb 14 10:02:22 hostname.domain.com sshd[10473]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:22 hostname.domain.com sshd[10475]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:22 hostname.domain.com sshd[10473]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:22 hostname.domain.com systemd-logind[737]: Removed session 6467487.
Feb 14 10:02:23 hostname.domain.com sshd[10484]: Accepted publickey for tropicg9 from 1.2.3.4 port 45294 ssh2: RSA 0b
Feb 14 10:02:23 hostname.domain.com systemd-logind[737]: New session 6467488 of user tropicg9.
Feb 14 10:02:23 hostname.domain.com systemd[1]: Started Session 6467488 of user tropicg9.
Feb 14 10:02:23 hostname.domain.com systemd[1]: Starting Session 6467488 of user tropicg9.
Feb 14 10:02:23 hostname.domain.com sshd[10484]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:23 hostname.domain.com sshd[10486]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:23 hostname.domain.com sshd[10484]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:23 hostname.domain.com systemd-logind[737]: Removed session 6467488.
Feb 14 10:02:39 hostname.domain.com sshd[10654]: Accepted publickey for tropicg9 from 1.2.3.4 port 45295 ssh2: RSA 0b
Feb 14 10:02:39 hostname.domain.com systemd[1]: Started Session 6467489 of user tropicg9.
Feb 14 10:02:39 hostname.domain.com systemd-logind[737]: New session 6467489 of user tropicg9.
Feb 14 10:02:39 hostname.domain.com systemd[1]: Starting Session 6467489 of user tropicg9.
Feb 14 10:02:39 hostname.domain.com sshd[10654]: pam_unix(sshd:session): session opened for user tropicg9 by (uid=0)
Feb 14 10:02:39 hostname.domain.com sshd[10656]: Received disconnect from 1.2.3.4: 11: disconnected by user
Feb 14 10:02:39 hostname.domain.com sshd[10654]: pam_unix(sshd:session): session closed for user tropicg9
Feb 14 10:02:39 hostname.domain.com systemd-logind[737]: Removed session 6467489.session 6467489.

Update 2-16-16

Here is output from systemd-cgtop showing resource usage for active control groups (scroll to the right). This shows all of the heavy resource usage under the "root" path. This does not seem to narrow it down, but perhaps this information could be helpful.

There are only 86 scope files and associated directories under /run/systemd/system/, up to 6 days old. There was an issue where these files were orphaned during SSH connections resulting in thousands of entries and high CPU load, but that is not happening here.

Path                                                                          Tasks   %CPU   Memory  Input/s Output/s

/                                                                               296   30.5    11.3G   657.8K   893.0K
/system.slice/NetworkManager.service                                              1      -        -        -        -
/system.slice/auditd.service                                                      1      -        -        -        -
/system.slice/crond.service                                                       1      -        -        -        -
/system.slice/dbus.service                                                        1      -        -        -        -
/system.slice/irqbalance.service                                                  1      -        -        -        -
/system.slice/lvm2-lvmetad.service                                                1      -        -        -        -
/system.slice/mariadb.service                                                     2      -        -        -        -
/system.slice/nginx.service                                                      10      -        -        -        -
/system.slice/php-fpm.service                                                   101      -        -        -        -
/system.slice/polkit.service                                                      1      -        -        -        -
/system.slice/postfix.service                                                     3      -        -        -        -
/system.slice/rsyslog.service                                                     1      -        -        -        -
/system.slice/smartd.service                                                      1      -        -        -        -
/system.slice/sshd.service                                                        2      -        -        -        -
/system.slice/system-getty.slice/getty@tty1.service                               1      -        -        -        -
/system.slice/systemd-journald.service                                            1      -        -        -        -
/system.slice/systemd-logind.service                                              1      -        -        -        -
/system.slice/systemd-udevd.service                                               1      -        -        -        -
/system.slice/tuned.service                                                       1      -        -        -        -
/system.slice/wpa_supplicant.service                                              1      -        -        -        -
/user.slice/user-1000.slice/session-7170741.scope                                 4      -        -        -        -

Temporary Clearing of systemd Memory

It appears that running systemctl daemon-reexec will release all memory allocated to the PID 1 process. However, the leak continues. A stop-gap solution to this problem is to set a daily cron to clear the memory, but it does not fix the leak. I've submitted a bug to Redhat since this is the stable release version of systemd for CentOS 7.x. Hopefully the leak can be found and plugged.

  • This may not be related, but what is the current disk (memory) usage of /run ? – Aaron Feb 12 '16 at 16:43
  • Have you kept the system up to date? – Michael Hampton Feb 12 '16 at 16:55
  • @Aaron Currently using 11% of the 7GB /run partition. None of the root-level system partitions are close to full. – meridionaljet Feb 12 '16 at 17:03
  • 3
    Sorry, we don't know that, because it was not in your question. – Michael Hampton Feb 12 '16 at 17:08
  • 3
    There was a PAM related memory leak in systemd recently when using socket activation. Could that be it? github.com/systemd/systemd/issues/2187 – Matt Feb 15 '16 at 0:25
2

Check the trace of systemd process for mmap/mmunmap calls. It should reveal the problem:

yum install strace
strace -ff -p 1

It's a quick and dirty way to diagnose memory leaks. Strace of systemd process should look similiar:

recvmsg(23, {msg_name(0)=NULL, msg_iov(1)=[{"WATCHDOG=1", 4096}], msg_controllen=32, {cmsg_len=28, cmsg_level=SOL_SOCKET, cmsg_type=SCM_CREDENTIALS{pid=620, uid=0, gid=0}}, msg_flags=MSG_CMSG_CLOEXEC}, MSG_DONTWAIT|MSG_CMSG_CLOEXEC) = 10
open("/proc/620/cgroup", O_RDONLY|O_CLOEXEC) = 20
fstat(20, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fcfd734e000
read(20, "10:cpuset:/\n9:perf_event:/\n8:hug"..., 1024) = 164
close(20)                               = 0
munmap(0x7fcfd734e000, 4096)            = 0

It allocates memory, does something, than releases memory.
Checking the trace of system calls systemd does, you should discover where it can't finish calls and release allocated memory.
I suppose there's a problem with improperly mounted pseudo-filesystems or selinux, so systemd can't finish its calls.

  • I have straced the process before, but the output for mmap calls is very vague (and numerous), and I personally don't know how to use it to track down a potential leak. – meridionaljet Feb 16 '16 at 18:33
  • 1
    I modified my answer with better explanation of strace use. – anx Feb 17 '16 at 10:38
  • 2
    the backside of having complicated init tool – asdmin Jun 30 '16 at 6:55

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