I seem to have about 10Gb of shared memory consumed, I believe by a process that I terminated with ctrl-C.

$ free -h
              total        used        free      shared  buff/cache   available
Mem:           31Gi       706Mi       1.9Gi        10Gi        28Gi        19Gi
Swap:         4.0Gi       4.0Gi          0B

Here's the output of htop, sorted on % memory use:

enter image description here

There do not seem to be any processes that can account for this. I definitely had a memory intensive program running at one point, but as mention I killed it. I'd like to run it again, but it's now unable to run because of memory issues. In addition, I checked

$ ipcs -a --human

------ Message Queues --------
key        msqid      owner      perms      size         messages

------ Shared Memory Segments --------
key        shmid      owner      perms      size       nattch     status
0x00000000 13         kevin      600            4M     2          dest
0x00000000 48         kevin      600            4M     2          dest
0x00000000 49         kevin      600           64M     2          dest

------ Semaphore Arrays --------
key        semid      owner      perms      nsems


I can reboot the system of course, but it's a server at work, and I don't always have physical access to start it back up. Is there a way to force that memory to be freed?

  • 1
    tmpfs (eg mounted on /tmp also /run /run/user/* etc.) uses shared memory – A.B Feb 8 '20 at 12:31

You may try:

echo 3 > /proc/sys/vm/drop_caches

This will clear system buffer and cache. Better if done when server is not under heavy workload.

  • I tried this a bit earlier based on some other posts here and didn't notice any change :-(. – kevbonham Feb 8 '20 at 1:57
  • What kind of job does this server do? Webserver? – realpclaudio Feb 8 '20 at 1:59
  • No, it's a linux desktop I use for scientific computing, but I usually ssh in from my mac – kevbonham Feb 8 '20 at 15:04
  • Did you tune some kernel parameters? That swap usage with plenty of ram still available is strange too. – realpclaudio Feb 8 '20 at 20:59
  • I didn't (at least, I don't think I did). If it makes a difference, it's running Pop!_os (which I think is mostly Ubuntu). But this is my first real experience with running a linux OS, so I've avoided messing about with anything low level. – kevbonham Feb 10 '20 at 14:26

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