p_candebug(9) manual page

[`EPERM`]
	An unprivileged process attempted to debug another process but the system is configured to deny it ( see sysctl(8) variable security.bsd.unprivileged_proc_debug above ).
[`ESRCH`]
	Thread td has been jailed and the process to debug does not belong to the same jail or one of its sub-jails, as determined by prison_check(9).
[`ESRCH`]
	cr_bsd_visible(9) denied visibility according to the BSD security policies in force.
[`EPERM`]
	Thread td lacks superuser credentials and its (effective) group set is not a superset of process p, Ns, 's whole group set (including real, effective and saved group IDs).
[`EPERM`]
	Thread td lacks superuser credentials and its (effective) user ID does not match all user IDs of process p.
[`EPERM`]
	Thread td lacks superuser credentials and process p is executing a set-user-ID or set-group-ID executable.
[`EPERM`]
	Process p denotes the initial process `initproc()` and the sysctl(8) variable kern.securelevel is greater than zero.
[`EBUSY`]
	Process p is in the process of being `exec()`'ed.
[`EPERM`]
	Process p denied debuggability ( see procctl(2), command `PROC_TRACE_CTL` ).

“	Computer science would have progressed much further and faster if all of the time and effort that has been spent maintaining and nurturing Unix had been spent on a sounder operating system.	”
— The Unix Haters' handbook

Manual Pages — P_CANDEBUG

security.bsd.unprivileged_proc_debug
	Must be set to a non-zero value to allow unprivileged processes access to the kernel's debug facilities.
kern.securelevel
	Debugging of the init process is not allowed if this variable is `1` or greater.