Where does Linux set the default values for SHMMAX?
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I'm just wondering where these values are being set and what they default to? Mine is currently 18446744073692774399. I didn't set it anywhere that I can see.
$ cat /proc/sys/kernel/shmmax
18446744073692774399
$ sysctl kernel.shmmax
kernel.shmmax = 18446744073692774399
kernel memory shared-memory
asked Jun 14 '17 at 0:47
Evan Carroll
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up vote
6
down vote
favorite
I'm just wondering where these values are being set and what they default to? Mine is currently 18446744073692774399. I didn't set it anywhere that I can see.
$ cat /proc/sys/kernel/shmmax
18446744073692774399
$ sysctl kernel.shmmax
kernel.shmmax = 18446744073692774399
kernel memory shared-memory
asked Jun 14 '17 at 0:47
Evan Carroll
4,47683472
add a comment |Â
up vote
6
down vote
favorite
up vote
6
down vote
favorite
I'm just wondering where these values are being set and what they default to? Mine is currently 18446744073692774399. I didn't set it anywhere that I can see.
$ cat /proc/sys/kernel/shmmax
18446744073692774399
$ sysctl kernel.shmmax
kernel.shmmax = 18446744073692774399
kernel memory shared-memory
asked Jun 14 '17 at 0:47
Evan Carroll
4,47683472
I'm just wondering where these values are being set and what they default to? Mine is currently 18446744073692774399. I didn't set it anywhere that I can see.
$ cat /proc/sys/kernel/shmmax
18446744073692774399
$ sysctl kernel.shmmax
kernel.shmmax = 18446744073692774399
kernel memory shared-memory
asked Jun 14 '17 at 0:47
Evan Carroll
4,47683472
asked Jun 14 '17 at 0:47
Evan Carroll
4,47683472
asked Jun 14 '17 at 0:47
Evan Carroll
4,47683472
asked Jun 14 '17 at 0:47
Evan Carroll
4,47683472
4,47683472
add a comment |Â
add a comment |Â
2 Answers
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The __init function ipc_ns_init sets the initial value of shmmax by calling shm_init_ns, which sets it to the value of the SHMMAX macro.
The definition of SHMMAX is in <uapi/linux/shm.h>:
#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
On 64-bit machines, that definition equals the value you found, 18446744073692774399.
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
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On the fly you can just echo into /proc/sys/kernel/shmmax!
# echo 20446744073692774399 > /proc/sys/kernel/shmmax
But most people edit /etc/sysctl.conf with a line similar to:
kernel.shmmax=your_new_value_here
See the sysctl(8) man page.
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
That's not the question. Where are the defaults set? That is, if you don't write to shmmax yourself, what does it default to?
– Evan Carroll
Jun 14 '17 at 2:09
1
On some Linux distros (RHEL 5&6 I believe is one) it is set in /etc/sysctl.conf. But I think the default is set in the kernel code to the theoretical limit (guessing that's 2^64 - 1?).
– Deathgrip
Jun 14 '17 at 2:48
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
5
down vote
accepted
The __init function ipc_ns_init sets the initial value of shmmax by calling shm_init_ns, which sets it to the value of the SHMMAX macro.
The definition of SHMMAX is in <uapi/linux/shm.h>:
#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
On 64-bit machines, that definition equals the value you found, 18446744073692774399.
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
add a comment |Â
up vote
5
down vote
accepted
The __init function ipc_ns_init sets the initial value of shmmax by calling shm_init_ns, which sets it to the value of the SHMMAX macro.
The definition of SHMMAX is in <uapi/linux/shm.h>:
#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
On 64-bit machines, that definition equals the value you found, 18446744073692774399.
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
add a comment |Â
up vote
5
down vote
accepted
up vote
5
down vote
accepted
The __init function ipc_ns_init sets the initial value of shmmax by calling shm_init_ns, which sets it to the value of the SHMMAX macro.
The definition of SHMMAX is in <uapi/linux/shm.h>:
#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
On 64-bit machines, that definition equals the value you found, 18446744073692774399.
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
The __init function ipc_ns_init sets the initial value of shmmax by calling shm_init_ns, which sets it to the value of the SHMMAX macro.
The definition of SHMMAX is in <uapi/linux/shm.h>:
#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
On 64-bit machines, that definition equals the value you found, 18446744073692774399.
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
answered Jun 14 '17 at 2:40
Wumpus Q. Wumbley
4,0001119
4,0001119
add a comment |Â
add a comment |Â
up vote
0
down vote
On the fly you can just echo into /proc/sys/kernel/shmmax!
# echo 20446744073692774399 > /proc/sys/kernel/shmmax
But most people edit /etc/sysctl.conf with a line similar to:
kernel.shmmax=your_new_value_here
See the sysctl(8) man page.
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
That's not the question. Where are the defaults set? That is, if you don't write to shmmax yourself, what does it default to?
– Evan Carroll
Jun 14 '17 at 2:09
1
On some Linux distros (RHEL 5&6 I believe is one) it is set in /etc/sysctl.conf. But I think the default is set in the kernel code to the theoretical limit (guessing that's 2^64 - 1?).
– Deathgrip
Jun 14 '17 at 2:48
add a comment |Â
up vote
0
down vote
On the fly you can just echo into /proc/sys/kernel/shmmax!
# echo 20446744073692774399 > /proc/sys/kernel/shmmax
But most people edit /etc/sysctl.conf with a line similar to:
kernel.shmmax=your_new_value_here
See the sysctl(8) man page.
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
That's not the question. Where are the defaults set? That is, if you don't write to shmmax yourself, what does it default to?
– Evan Carroll
Jun 14 '17 at 2:09
1
On some Linux distros (RHEL 5&6 I believe is one) it is set in /etc/sysctl.conf. But I think the default is set in the kernel code to the theoretical limit (guessing that's 2^64 - 1?).
– Deathgrip
Jun 14 '17 at 2:48
add a comment |Â
up vote
0
down vote
up vote
0
down vote
On the fly you can just echo into /proc/sys/kernel/shmmax!
# echo 20446744073692774399 > /proc/sys/kernel/shmmax
But most people edit /etc/sysctl.conf with a line similar to:
kernel.shmmax=your_new_value_here
See the sysctl(8) man page.
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
On the fly you can just echo into /proc/sys/kernel/shmmax!
# echo 20446744073692774399 > /proc/sys/kernel/shmmax
But most people edit /etc/sysctl.conf with a line similar to:
kernel.shmmax=your_new_value_here
See the sysctl(8) man page.
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
answered Jun 14 '17 at 1:47
Deathgrip
1,266311
1,266311
That's not the question. Where are the defaults set? That is, if you don't write to shmmax yourself, what does it default to?
– Evan Carroll
Jun 14 '17 at 2:09
1
On some Linux distros (RHEL 5&6 I believe is one) it is set in /etc/sysctl.conf. But I think the default is set in the kernel code to the theoretical limit (guessing that's 2^64 - 1?).
– Deathgrip
Jun 14 '17 at 2:48
add a comment |Â
That's not the question. Where are the defaults set? That is, if you don't write to shmmax yourself, what does it default to?
– Evan Carroll
Jun 14 '17 at 2:09
1
On some Linux distros (RHEL 5&6 I believe is one) it is set in /etc/sysctl.conf. But I think the default is set in the kernel code to the theoretical limit (guessing that's 2^64 - 1?).
– Deathgrip
Jun 14 '17 at 2:48
That's not the question. Where are the defaults set? That is, if you don't write to shmmax yourself, what does it default to?
– Evan Carroll
Jun 14 '17 at 2:09
That's not the question. Where are the defaults set? That is, if you don't write to shmmax yourself, what does it default to?
– Evan Carroll
Jun 14 '17 at 2:09
1
1
On some Linux distros (RHEL 5&6 I believe is one) it is set in /etc/sysctl.conf. But I think the default is set in the kernel code to the theoretical limit (guessing that's 2^64 - 1?).
– Deathgrip
Jun 14 '17 at 2:48
On some Linux distros (RHEL 5&6 I believe is one) it is set in /etc/sysctl.conf. But I think the default is set in the kernel code to the theoretical limit (guessing that's 2^64 - 1?).
– Deathgrip
Jun 14 '17 at 2:48
add a comment |Â
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