Solved sysctl: tunable values are set in …

[Cath O'Deray]

Use sysctl command to enable or disable (after booting into system)

sysctl kern.smp.disabled
sysctl kern.smp.disabled=0
sysctl kern.smp.disabled=1

Where, 0 - off / false and 1 - on / true. To make it permanent …

I did expect the command to fail, I did not expect this:

root@mowa219-gjp4-8570p-freebsd:~ # sysctl kern.smp.disabled=1
sysctl: oid 'kern.smp.disabled' is a read only tunable
sysctl: Tunable values are set in /boot/loader.conf
root@mowa219-gjp4-8570p-freebsd:~ #

As far as I know, /etc/sysctl.conf should be preferred. True or false?

loader.conf

sysctl.conf

 

[covacat]

some can only be set before the kernel boots (loader.conf), some only after the kernel boots, some in both places
look at -W and -T flags of sysctl(8)

 

[Cath O'Deray]

I mean, is the direction (the response from sysctl) outdated?

Tunable values are set in /boot/loader.conf

 

[covacat]

the readonly tunables can only be set in loader.conf
for the rw ones it depends on the use case

 

[Cath O'Deray]

Thanks.

I just discovered that yesterday, I had a misleading test result with this particular tunable in /etc/sysctl.conf (not in /boot/loader.conf)

• the tunable was in the wrong file
• despite the wrong placement, I did get the required effect – symmetric multiprocessor support was disabled

– htop(1) presented just one CPU.

smp(4)

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I could share a likely explanation for the misleading result, but readers might not understand the explanation, so I'll keep it to myself and mark this topic Solved.