What is the meaning of `shared` memory in the `free` command?
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The fourth column in the output of free is named shared. On most outputs I can see in internet, the shared memory is zero. But that's not the case on my computer:
$ free -h
total used free shared buff/cache available
Mem: 7,7G 3,8G 1,1G 611M 2,8G 3,0G
Swap: 3,8G 0B 3,8G
Here is also an excerpt of the output of ps_mem.py:
Private + Shared = RAM used Program
---------------------------------
21.4 MiB + 1.0 MiB = 22.4 MiB bash (9)
29.2 MiB + 5.3 MiB = 34.5 MiB Xorg
35.9 MiB + 858.5 KiB = 36.7 MiB tor
42.9 MiB + 9.6 MiB = 52.5 MiB urxvt (16)
121.0 MiB + 24.9 MiB = 145.8 MiB okular (2)
151.8 MiB + 2.8 MiB = 154.6 MiB soffice.bin
3.7 GiB + 209.3 MiB = 4.0 GiB chromium (39)
---------------------------------
4.6 GiB
=================================
What is the meaning of a shared memory?
Main answer in the Question 14102 says: shared: a concept that no longer exists. It's left in the output for backward compatibility. Looks insufficient to me. A "non-existent" concept does not take 600+ MB of RAM.
linux memory ram
edited Nov 19 at 16:33
sourcejedi
21.9k43396
asked Aug 31 '16 at 16:45
BertS
17118
add a comment |
up vote
5
down vote
favorite
The fourth column in the output of free is named shared. On most outputs I can see in internet, the shared memory is zero. But that's not the case on my computer:
$ free -h
total used free shared buff/cache available
Mem: 7,7G 3,8G 1,1G 611M 2,8G 3,0G
Swap: 3,8G 0B 3,8G
Here is also an excerpt of the output of ps_mem.py:
Private + Shared = RAM used Program
---------------------------------
21.4 MiB + 1.0 MiB = 22.4 MiB bash (9)
29.2 MiB + 5.3 MiB = 34.5 MiB Xorg
35.9 MiB + 858.5 KiB = 36.7 MiB tor
42.9 MiB + 9.6 MiB = 52.5 MiB urxvt (16)
121.0 MiB + 24.9 MiB = 145.8 MiB okular (2)
151.8 MiB + 2.8 MiB = 154.6 MiB soffice.bin
3.7 GiB + 209.3 MiB = 4.0 GiB chromium (39)
---------------------------------
4.6 GiB
=================================
What is the meaning of a shared memory?
Main answer in the Question 14102 says: shared: a concept that no longer exists. It's left in the output for backward compatibility. Looks insufficient to me. A "non-existent" concept does not take 600+ MB of RAM.
linux memory ram
edited Nov 19 at 16:33
sourcejedi
21.9k43396
asked Aug 31 '16 at 16:45
BertS
17118
4
Possible duplicate of real memory usage
– Tomasz
Aug 31 '16 at 18:45
have you triedman free?
– Archemar
Sep 1 '16 at 8:41
@Archemar manpage says: "shared: Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)". That is not very clear; I'd like a more elaborate explanation.
– BertS
Sep 1 '16 at 15:06
add a comment |
up vote
5
down vote
favorite
up vote
5
down vote
favorite
The fourth column in the output of free is named shared. On most outputs I can see in internet, the shared memory is zero. But that's not the case on my computer:
$ free -h
total used free shared buff/cache available
Mem: 7,7G 3,8G 1,1G 611M 2,8G 3,0G
Swap: 3,8G 0B 3,8G
Here is also an excerpt of the output of ps_mem.py:
Private + Shared = RAM used Program
---------------------------------
21.4 MiB + 1.0 MiB = 22.4 MiB bash (9)
29.2 MiB + 5.3 MiB = 34.5 MiB Xorg
35.9 MiB + 858.5 KiB = 36.7 MiB tor
42.9 MiB + 9.6 MiB = 52.5 MiB urxvt (16)
121.0 MiB + 24.9 MiB = 145.8 MiB okular (2)
151.8 MiB + 2.8 MiB = 154.6 MiB soffice.bin
3.7 GiB + 209.3 MiB = 4.0 GiB chromium (39)
---------------------------------
4.6 GiB
=================================
What is the meaning of a shared memory?
Main answer in the Question 14102 says: shared: a concept that no longer exists. It's left in the output for backward compatibility. Looks insufficient to me. A "non-existent" concept does not take 600+ MB of RAM.
linux memory ram
edited Nov 19 at 16:33
sourcejedi
21.9k43396
asked Aug 31 '16 at 16:45
BertS
17118
The fourth column in the output of free is named shared. On most outputs I can see in internet, the shared memory is zero. But that's not the case on my computer:
$ free -h
total used free shared buff/cache available
Mem: 7,7G 3,8G 1,1G 611M 2,8G 3,0G
Swap: 3,8G 0B 3,8G
Here is also an excerpt of the output of ps_mem.py:
Private + Shared = RAM used Program
---------------------------------
21.4 MiB + 1.0 MiB = 22.4 MiB bash (9)
29.2 MiB + 5.3 MiB = 34.5 MiB Xorg
35.9 MiB + 858.5 KiB = 36.7 MiB tor
42.9 MiB + 9.6 MiB = 52.5 MiB urxvt (16)
121.0 MiB + 24.9 MiB = 145.8 MiB okular (2)
151.8 MiB + 2.8 MiB = 154.6 MiB soffice.bin
3.7 GiB + 209.3 MiB = 4.0 GiB chromium (39)
---------------------------------
4.6 GiB
=================================
What is the meaning of a shared memory?
Main answer in the Question 14102 says: shared: a concept that no longer exists. It's left in the output for backward compatibility. Looks insufficient to me. A "non-existent" concept does not take 600+ MB of RAM.
linux memory ram
linux memory ram
edited Nov 19 at 16:33
sourcejedi
21.9k43396
asked Aug 31 '16 at 16:45
BertS
17118
edited Nov 19 at 16:33
sourcejedi
21.9k43396
asked Aug 31 '16 at 16:45
BertS
17118
edited Nov 19 at 16:33
sourcejedi
21.9k43396
edited Nov 19 at 16:33
sourcejedi
21.9k43396
edited Nov 19 at 16:33
sourcejedi
21.9k43396
21.9k43396
asked Aug 31 '16 at 16:45
BertS
17118
asked Aug 31 '16 at 16:45
BertS
17118
asked Aug 31 '16 at 16:45
BertS
17118
17118
4
Possible duplicate of real memory usage
– Tomasz
Aug 31 '16 at 18:45
have you triedman free?
– Archemar
Sep 1 '16 at 8:41
@Archemar manpage says: "shared: Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)". That is not very clear; I'd like a more elaborate explanation.
– BertS
Sep 1 '16 at 15:06
add a comment |
4
Possible duplicate of real memory usage
– Tomasz
Aug 31 '16 at 18:45
have you triedman free?
– Archemar
Sep 1 '16 at 8:41
@Archemar manpage says: "shared: Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)". That is not very clear; I'd like a more elaborate explanation.
– BertS
Sep 1 '16 at 15:06
4
4
Possible duplicate of real memory usage
– Tomasz
Aug 31 '16 at 18:45
Possible duplicate of real memory usage
– Tomasz
Aug 31 '16 at 18:45
have you tried
man free ?– Archemar
Sep 1 '16 at 8:41
have you tried
man free ?– Archemar
Sep 1 '16 at 8:41
@Archemar manpage says: "shared: Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)". That is not very clear; I'd like a more elaborate explanation.
– BertS
Sep 1 '16 at 15:06
@Archemar manpage says: "shared: Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)". That is not very clear; I'd like a more elaborate explanation.
– BertS
Sep 1 '16 at 15:06
add a comment |
1 Answer
1
active
oldest
votes
up vote
3
down vote
"Shared" in free and "Shmem" in /proc/meminfo count all the memory used by the tmpfs file system (a file system in the memory) and also the shared memory (allocated by shmget(2)).
This is documented in https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt.
Here is an example from one of my servers:
$ free -k
total used free shared buff/cache available
Mem: 264036296 1275384 254696692 1182024 8064220 260536208
Swap: 63998972 0 63998972
$ grep Shmem /proc/meminfo
Shmem: 1182024 kB
$ df -BK | grep tmpfs
tmpfs 26403632K 51424K 26352208K 1% /run
tmpfs 132018148K 224K 132017924K 1% /dev/shm
tmpfs 5120K 4K 5116K 1% /run/lock
tmpfs 132018148K 0K 132018148K 0% /sys/fs/cgroup
tmpfs 251658240K 1129036K 250529204K 1% /run/shm
tmpfs 26403632K 24K 26403608K 1% /run/user/108
tmpfs 26403632K 0K 26403632K 0% /run/user/5800006
If you sum up the used size (3rd column) of all tmpfs filesystems listed by df, you will find the sum is equal to "shared" and "shmem".
answered Jan 16 at 13:25
lqhl
313
Thanks for explaining, but are thosetmpfsare needed, Can I delete them and if possible how do I delete them?. I have encounter this issue many times after waking up the system from hibernation(~4GB is taken byshared)
– Kasun Siyambalapitiya
Oct 19 at 5:19
Hi @KasunSiyambalapitiya. Shmem also includes GEM graphics buffers, as per kernel source comments and lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/… . Some previous versions of systemd had a bug that leaked graphics buffers (seriously) when the graphics server exited... that was "fun". unix.stackexchange.com/questions/431982/… . That specific problem could only apply if your entire graphical session has been crashing, or if you have deliberately logged out of your whole session (and back in again).
– sourcejedi
Nov 19 at 16:44
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
"Shared" in free and "Shmem" in /proc/meminfo count all the memory used by the tmpfs file system (a file system in the memory) and also the shared memory (allocated by shmget(2)).
This is documented in https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt.
Here is an example from one of my servers:
$ free -k
total used free shared buff/cache available
Mem: 264036296 1275384 254696692 1182024 8064220 260536208
Swap: 63998972 0 63998972
$ grep Shmem /proc/meminfo
Shmem: 1182024 kB
$ df -BK | grep tmpfs
tmpfs 26403632K 51424K 26352208K 1% /run
tmpfs 132018148K 224K 132017924K 1% /dev/shm
tmpfs 5120K 4K 5116K 1% /run/lock
tmpfs 132018148K 0K 132018148K 0% /sys/fs/cgroup
tmpfs 251658240K 1129036K 250529204K 1% /run/shm
tmpfs 26403632K 24K 26403608K 1% /run/user/108
tmpfs 26403632K 0K 26403632K 0% /run/user/5800006
If you sum up the used size (3rd column) of all tmpfs filesystems listed by df, you will find the sum is equal to "shared" and "shmem".
answered Jan 16 at 13:25
lqhl
313
Thanks for explaining, but are thosetmpfsare needed, Can I delete them and if possible how do I delete them?. I have encounter this issue many times after waking up the system from hibernation(~4GB is taken byshared)
– Kasun Siyambalapitiya
Oct 19 at 5:19
Hi @KasunSiyambalapitiya. Shmem also includes GEM graphics buffers, as per kernel source comments and lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/… . Some previous versions of systemd had a bug that leaked graphics buffers (seriously) when the graphics server exited... that was "fun". unix.stackexchange.com/questions/431982/… . That specific problem could only apply if your entire graphical session has been crashing, or if you have deliberately logged out of your whole session (and back in again).
– sourcejedi
Nov 19 at 16:44
add a comment |
up vote
3
down vote
"Shared" in free and "Shmem" in /proc/meminfo count all the memory used by the tmpfs file system (a file system in the memory) and also the shared memory (allocated by shmget(2)).
This is documented in https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt.
Here is an example from one of my servers:
$ free -k
total used free shared buff/cache available
Mem: 264036296 1275384 254696692 1182024 8064220 260536208
Swap: 63998972 0 63998972
$ grep Shmem /proc/meminfo
Shmem: 1182024 kB
$ df -BK | grep tmpfs
tmpfs 26403632K 51424K 26352208K 1% /run
tmpfs 132018148K 224K 132017924K 1% /dev/shm
tmpfs 5120K 4K 5116K 1% /run/lock
tmpfs 132018148K 0K 132018148K 0% /sys/fs/cgroup
tmpfs 251658240K 1129036K 250529204K 1% /run/shm
tmpfs 26403632K 24K 26403608K 1% /run/user/108
tmpfs 26403632K 0K 26403632K 0% /run/user/5800006
If you sum up the used size (3rd column) of all tmpfs filesystems listed by df, you will find the sum is equal to "shared" and "shmem".
answered Jan 16 at 13:25
lqhl
313
Thanks for explaining, but are thosetmpfsare needed, Can I delete them and if possible how do I delete them?. I have encounter this issue many times after waking up the system from hibernation(~4GB is taken byshared)
– Kasun Siyambalapitiya
Oct 19 at 5:19
Hi @KasunSiyambalapitiya. Shmem also includes GEM graphics buffers, as per kernel source comments and lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/… . Some previous versions of systemd had a bug that leaked graphics buffers (seriously) when the graphics server exited... that was "fun". unix.stackexchange.com/questions/431982/… . That specific problem could only apply if your entire graphical session has been crashing, or if you have deliberately logged out of your whole session (and back in again).
– sourcejedi
Nov 19 at 16:44
add a comment |
up vote
3
down vote
up vote
3
down vote
"Shared" in free and "Shmem" in /proc/meminfo count all the memory used by the tmpfs file system (a file system in the memory) and also the shared memory (allocated by shmget(2)).
This is documented in https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt.
Here is an example from one of my servers:
$ free -k
total used free shared buff/cache available
Mem: 264036296 1275384 254696692 1182024 8064220 260536208
Swap: 63998972 0 63998972
$ grep Shmem /proc/meminfo
Shmem: 1182024 kB
$ df -BK | grep tmpfs
tmpfs 26403632K 51424K 26352208K 1% /run
tmpfs 132018148K 224K 132017924K 1% /dev/shm
tmpfs 5120K 4K 5116K 1% /run/lock
tmpfs 132018148K 0K 132018148K 0% /sys/fs/cgroup
tmpfs 251658240K 1129036K 250529204K 1% /run/shm
tmpfs 26403632K 24K 26403608K 1% /run/user/108
tmpfs 26403632K 0K 26403632K 0% /run/user/5800006
If you sum up the used size (3rd column) of all tmpfs filesystems listed by df, you will find the sum is equal to "shared" and "shmem".
answered Jan 16 at 13:25
lqhl
313
"Shared" in free and "Shmem" in /proc/meminfo count all the memory used by the tmpfs file system (a file system in the memory) and also the shared memory (allocated by shmget(2)).
This is documented in https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt.
Here is an example from one of my servers:
$ free -k
total used free shared buff/cache available
Mem: 264036296 1275384 254696692 1182024 8064220 260536208
Swap: 63998972 0 63998972
$ grep Shmem /proc/meminfo
Shmem: 1182024 kB
$ df -BK | grep tmpfs
tmpfs 26403632K 51424K 26352208K 1% /run
tmpfs 132018148K 224K 132017924K 1% /dev/shm
tmpfs 5120K 4K 5116K 1% /run/lock
tmpfs 132018148K 0K 132018148K 0% /sys/fs/cgroup
tmpfs 251658240K 1129036K 250529204K 1% /run/shm
tmpfs 26403632K 24K 26403608K 1% /run/user/108
tmpfs 26403632K 0K 26403632K 0% /run/user/5800006
If you sum up the used size (3rd column) of all tmpfs filesystems listed by df, you will find the sum is equal to "shared" and "shmem".
answered Jan 16 at 13:25
lqhl
313
answered Jan 16 at 13:25
lqhl
313
answered Jan 16 at 13:25
lqhl
313
answered Jan 16 at 13:25
lqhl
313
313
Thanks for explaining, but are thosetmpfsare needed, Can I delete them and if possible how do I delete them?. I have encounter this issue many times after waking up the system from hibernation(~4GB is taken byshared)
– Kasun Siyambalapitiya
Oct 19 at 5:19
Hi @KasunSiyambalapitiya. Shmem also includes GEM graphics buffers, as per kernel source comments and lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/… . Some previous versions of systemd had a bug that leaked graphics buffers (seriously) when the graphics server exited... that was "fun". unix.stackexchange.com/questions/431982/… . That specific problem could only apply if your entire graphical session has been crashing, or if you have deliberately logged out of your whole session (and back in again).
– sourcejedi
Nov 19 at 16:44
add a comment |
Thanks for explaining, but are thosetmpfsare needed, Can I delete them and if possible how do I delete them?. I have encounter this issue many times after waking up the system from hibernation(~4GB is taken byshared)
– Kasun Siyambalapitiya
Oct 19 at 5:19
Hi @KasunSiyambalapitiya. Shmem also includes GEM graphics buffers, as per kernel source comments and lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/… . Some previous versions of systemd had a bug that leaked graphics buffers (seriously) when the graphics server exited... that was "fun". unix.stackexchange.com/questions/431982/… . That specific problem could only apply if your entire graphical session has been crashing, or if you have deliberately logged out of your whole session (and back in again).
– sourcejedi
Nov 19 at 16:44
Thanks for explaining, but are those
tmpfs are needed, Can I delete them and if possible how do I delete them?. I have encounter this issue many times after waking up the system from hibernation(~4GB is taken by shared)– Kasun Siyambalapitiya
Oct 19 at 5:19
Thanks for explaining, but are those
tmpfs are needed, Can I delete them and if possible how do I delete them?. I have encounter this issue many times after waking up the system from hibernation(~4GB is taken by shared)– Kasun Siyambalapitiya
Oct 19 at 5:19
Hi @KasunSiyambalapitiya. Shmem also includes GEM graphics buffers, as per kernel source comments and lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/… . Some previous versions of systemd had a bug that leaked graphics buffers (seriously) when the graphics server exited... that was "fun". unix.stackexchange.com/questions/431982/… . That specific problem could only apply if your entire graphical session has been crashing, or if you have deliberately logged out of your whole session (and back in again).
– sourcejedi
Nov 19 at 16:44
Hi @KasunSiyambalapitiya. Shmem also includes GEM graphics buffers, as per kernel source comments and lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/… . Some previous versions of systemd had a bug that leaked graphics buffers (seriously) when the graphics server exited... that was "fun". unix.stackexchange.com/questions/431982/… . That specific problem could only apply if your entire graphical session has been crashing, or if you have deliberately logged out of your whole session (and back in again).
– sourcejedi
Nov 19 at 16:44
add a comment |
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4
Possible duplicate of real memory usage
– Tomasz
Aug 31 '16 at 18:45
have you tried
man free?– Archemar
Sep 1 '16 at 8:41
@Archemar manpage says: "shared: Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)". That is not very clear; I'd like a more elaborate explanation.
– BertS
Sep 1 '16 at 15:06