# com.startup.sysctl.plist

As of at least macOS Catalina 10.15.3, `/etc/sysctl.conf` values are no longer respected and/or the file straight up doesn't exist (confirmed on macOS Monterey 12.4.)

Ran across a `fio` shm error: `failed to setup shm segment` while benchmarking SSDs. The fix was to set `shmmni` to `4096`. The following has to happen:
* [Disable SIP](https://developer.apple.com/documentation/security/disabling_and_enabling_system_integrity_protection)
  * **Disclaimer from Apple**
    > Warning
    > 
    > Disable SIP only temporarily to perform necessary tasks, and reenable it as soon as possible. Failure to reenable SIP when you are done testing leaves your computer vulnerable to malicious code. 
* Download `com.startup.sysctl.plist`
* Move to `/Library/LaunchDaemons/com.startup.sysctl.plist`
* Load the PLIST after a few housekeeping items
    ```bash
    # sanity check
    sysctl -a | grep shm

    # set permissions
    sudo chown root:wheel /Library/LaunchDaemons/com.startup.sysctl.plist

    # validate key-value pairs
    plutil /Library/LaunchDaemons/com.startup.sysctl.plist

    # load plist
    sudo launchctl bootstrap system /Library/LaunchDaemons/com.startup.sysctl.plist

    # check logs
    tail -f /tmp/sysctl.out
    tail -f /tmp/sysctl.err

    # recheck sysctl values
    sysctl -a | grep shm
    ```
* If the `shmmni` or other values didn't change, a reboot is in order
  * Known good output when values are changed successfully
    ```
    λ tail -f /tmp/sysctl.out
    kern.sysv.shmmax: 4194304 -> 4194304
    kern.sysv.shmmin: 1 -> 1
    kern.sysv.shmmni: 32 -> 4096
    kern.sysv.shmseg: 8 -> 8
    kern.sysv.shmall: 1024 -> 1024
    λ sysctl -a | grep shm
    kern.sysv.shmmax: 4194304
    kern.sysv.shmmin: 1
    kern.sysv.shmmni: 4096
    kern.sysv.shmseg: 8
    kern.sysv.shmall: 1024
    security.mac.posixshm_enforce: 1
    security.mac.sysvshm_enforce: 1
    ```

## Sources
[macos - Values from sysctl -A don't match /etc/sysctl.conf even after restart - Unix & Linux Stack Exchange](https://unix.stackexchange.com/questions/689295/values-from-sysctl-a-dont-match-etc-sysctl-conf-even-after-restart)

[Setting shared memory in Catalina | Apple Developer Forums](https://developer.apple.com/forums/thread/669625)

[c++ - Shared memory "Too many open files" but ipcs doesn't show many allocations - Stack Overflow](https://stackoverflow.com/questions/70988547/shared-memory-too-many-open-files-but-ipcs-doesnt-show-many-allocations)

[kernel - How do I increase the max open files in macOS Big Sur? - Super User](https://superuser.com/questions/1634286/how-do-i-increase-the-max-open-files-in-macos-big-sur)

[A launchd Tutorial](https://www.launchd.info/)

[macos - Values from sysctl -A don't match /etc/sysctl.conf even after restart - Unix & Linux Stack Exchange](https://unix.stackexchange.com/questions/689295/values-from-sysctl-a-dont-match-etc-sysctl-conf-even-after-restart/710645)

[macos - "No space left on drive" when trying to allocate more shared memory - Stack Overflow](https://stackoverflow.com/questions/70884304/no-space-left-on-drive-when-trying-to-allocate-more-shared-memory/73058877)