DTRACE_PROC(4)

💅 DTRACE_PROC(4) — like, the whole manual page, bestie

Hey bestie, so this is a page from the Kernel Interfaces Manual (yes, that's the manual name, we're fancy now) and it's all about dtrace_proc — a DTrace provider for tracing events related to user processes. Strap in 🎀

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✨ SYNOPSIS ✨

Okay so here's the whole vibe, one probe at a time:

proc:::create(struct proc *, struct proc *, int);

proc:::exec(char *);

proc:::exec-failure(int);

proc:::exec-success(char *);

proc:::exit(int);

proc:::signal-clear(int, ksiginfo_t *);

proc:::signal-discard(struct thread *, struct proc *, int);

proc:::signal-send(struct thread *, struct proc *, int);

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🦋 DESCRIPTION 🦋

The DTrace proc provider gives you the inside scoop on user process events, like: process and thread creation and termination, and process signalling. Literally all the juicy process drama 🔥

The proc:::create() probe fires when a user process is created via the fork(2), vfork(2), pdfork(2), or rfork(2) system calls. Super important caveat tho: kernel processes created with the kproc(9) KPI will not trigger this probe, no cap. The proc:::create() probe's first two arguments are the new child process and its parent, respectively (so args[0] = baby, args[1] = parent, iykyk 👶). The third argument is a mask of rfork(2) flags indicating which process resources are to be shared between the parent and child processes.

The proc:::exec() probe fires when a process attempts to execute a file. Its argument is the specified filename for the file. If the attempt fails because of an error, the proc:::exec-failure() probe will subsequently fire, providing the corresponding errno(2) value in its first argument. Otherwise (success era ✨), the proc:::exec-success() probe will fire.

The proc:::exit() probe fires when a process exits or is terminated. Its argument is the corresponding SIGCHLD signal code; valid values are documented in the siginfo(3) manual page and defined in signal.h. For example, when a process exits normally, the value of args[0] will be CLD_EXITED. Slay, clean exit 💀

The proc:::signal-send() probe fires when a signal is about to be sent to a process. The proc:::signal-discard() probe fires when a signal is sent to a process that ignores it — rude of them tbh 🙈. This probe will fire after the proc:::signal-send() probe for the signal in question. The arguments to these probes are the thread and process to which the signal will be sent, and the signal number of the signal. Valid signal numbers are defined in the signal(3) manual page. The proc:::signal-clear() probe fires when a pending signal has been cleared by one of the sigwait(2), sigtimedwait(2), or sigwaitinfo(2) system calls. Its arguments are the signal number of the cleared signal, and a pointer to the corresponding signal information. You can get the siginfo_t for the signal from args[1]->ksi_info — yes, exactly like that, bestie 💖

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👑 ARGUMENTS 👑

Okay so even though the proc provider probes use native FreeBSD arguments types, standard D types for processes and threads are available 👏 These are psinfo_t and lwpsinfo_t respectively, and they're defined in /usr/lib/dtrace/psinfo.d. That file also defines two global variables, curpsinfo and curlwpsinfo, which provide representations of the current process and thread using these types. Iconic.

🌸 The fields of psinfo_t are:

• int pr_nlwp — Number of threads in the process.
• pid_t pr_pid — Process ID.
• pid_t pr_ppid — Process ID of the parent process, or 0 if the process does not have a parent.
• pid_t pr_pgid — Process ID of the process group leader.
• pid_t pr_sid — Session ID, or 0 if the process does not belong to a session.
• pid_t pr_uid — Real user ID.
• pid_t pr_euid — Effective user ID.
• pid_t pr_gid — Real group ID.
• pid_t pr_egid — Effective group ID.
• uintptr_t pr_addr — Pointer to the struct proc for the process.
• string pr_psargs — Process arguments.
• u_int pr_arglen — Length of the process argument string.
• u_int pr_jailid — Jail ID of the process.

🧚 The fields of lwpsinfo_t are:

• id_t pr_lwpid — Thread ID.
• int pr_flag — Thread flags.
• int pr_pri — Real scheduling priority of the thread.
• char pr_state — Currently always 0.
• char pr_sname — Currently always '?'.
• short pr_syscall — Currently always 0.
• uintptr_t pr_addr — Pointer to the struct thread for the thread.
• uintptr_t pr_wchan — Current wait address on which the thread is sleeping.

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🎀 FILES 🎀

• /usr/lib/dtrace/psinfo.d — DTrace type and translator definitions for the proc provider.

(That's the whole list. One file. She's lowkey carrying the entire operation 💅)

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⭐ EXAMPLES ⭐

The following script logs process execution events as they occur — copy it, run it, obsess over it:

#pragma D option quiet

proc:::exec-success
{
        printf("%s", curpsinfo->pr_psargs);
}

Heads up bestie: the pr_psargs field is subject to the limit defined by the kern.ps_arg_cache_limit sysctl. In particular, processes with an argument list longer than the value defined by this sysctl cannot be logged in this way. So if your args are too long, it's giving nothing, no data for you 😭

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💜 COMPATIBILITY 💜

The proc provider in FreeBSD is not compatible with the proc provider in Solaris. Not even a little. In particular, FreeBSD uses the native struct proc and struct thread types for probe arguments rather than translated types. Additionally, a number of proc provider probes found in Solaris are not currently available on FreeBSD. Different lore, different era 🌈

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🔥 SEE ALSO 🔥

dtrace(1), errno(2), fork(2), pdfork(2), rfork(2), vfork(2), siginfo(3), signal(3), dtrace_sched(4), kproc(9)

Read them all, bestie, they're all linked 💖

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🕰️ HISTORY 🕰️

The proc provider first appeared in FreeBSD 7.1. Vintage. Elder emoji energy 👑

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🫶 AUTHORS 🫶

This manual page was written by Mark Johnston <markj@FreeBSD.org>. Thank you Mark, king behavior 👑

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Okay that's the whole page babes!! Written for the Debian manual, dated March 3, 2023, filed under DTRACE_PROC(4) — go trace some processes, you got this, periodt ✨💅🎀