getrusage(2)

🌸 getrusage — the resource usage receipt bestie 💅

ok so real talk: this is getrusage(2), a system call (section 2, the cool section), and it's literally the function that hands you a lil receipt of how much CPU, memory, and I/O your program has been eating. pull up a chair 🫶

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✨ NAME ✨

getrusage — get resource usage. that's it, that's the whole vibe. it tells you what your process has been consuming. 💖

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📚 LIBRARY 📚

Standard C library (libc, link it with -lc) — so like, the normal one, nothing exotic, no cap.

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🎀 SYNOPSIS 🎀

#include <sys/resource.h>

int getrusage(int who, struct rusage *usage);

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💅 DESCRIPTION 💅

so getrusage() returns resource usage measures for who, and bestie, who can be one of these three icons:

• RUSAGE_SELF — returns the resource usage stats for the calling process, which is the sum of resources used by all the threads in that process. yes, all of them. the whole squad's tab. 👑
• RUSAGE_CHILDREN — returns the resource usage stats for all children of the calling process that have terminated and been waited for. and it gets messier: these stats also include the resources used by grandchildren, and even further-removed descendants, if all of the intervening descendants waited on their terminated children. family tree accounting, fr fr. 🌳
• RUSAGE_THREAD (since Linux 2.6.26) — returns the resource usage stats for the calling thread only. just you, main character energy. BUT ⚠️ you must define the _GNU_SOURCE feature test macro (before including any header file, do not play with me on this) in order to obtain the definition of this constant from <sys/resource.h>.

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🦋 the struct, look at her 🦋

the resource usages come back in the structure pointed to by usage, which has this exact form:

struct rusage {
    struct timeval ru_utime; /* user CPU time used */
    struct timeval ru_stime; /* system CPU time used */
    long   ru_maxrss;        /* maximum resident set size */
    long   ru_ixrss;         /* integral shared memory size */
    long   ru_idrss;         /* integral unshared data size */
    long   ru_isrss;         /* integral unshared stack size */
    long   ru_minflt;        /* page reclaims (soft page faults) */
    long   ru_majflt;        /* page faults (hard page faults) */
    long   ru_nswap;         /* swaps */
    long   ru_inblock;       /* block input operations */
    long   ru_oublock;       /* block output operations */
    long   ru_msgsnd;        /* IPC messages sent */
    long   ru_msgrcv;        /* IPC messages received */
    long   ru_nsignals;      /* signals received */
    long   ru_nvcsw;         /* voluntary context switches */
    long   ru_nivcsw;        /* involuntary context switches */
};

⚠️ important lore: not all fields are completed. unmaintained fields are set to zero by the kernel. (the unmaintained fields are there for compatibility with other systems, and because they may one day be supported on Linux — hope springs eternal 🥲.)

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💖 field-by-field, let's get into it 💖

• ru_utime — the total amount of time spent executing in user mode, expressed in a timeval structure (seconds plus microseconds).
• ru_stime — the total amount of time spent executing in kernel mode, expressed in a timeval structure (seconds plus microseconds).
• ru_maxrss (since Linux 2.6.32) — the maximum resident set size used, in KiB. and heads up: for RUSAGE_CHILDREN, this is the resident set size of the largest child, not the maximum resident set size of the whole process tree. don't let it gaslight you. 😭
• ru_ixrss (unmaintained) — this field is currently unused on Linux.
• ru_idrss (unmaintained) — this field is currently unused on Linux.
• ru_isrss (unmaintained) — this field is currently unused on Linux.
• ru_minflt — the number of page faults serviced without any I/O activity; here, I/O activity is avoided by “reclaiming” a page frame from the list of pages awaiting reallocation. recycling era ♻️
• ru_majflt — the number of page faults serviced that required I/O activity. the expensive ones. 💀
• ru_nswap (unmaintained) — this field is currently unused on Linux.
• ru_inblock (since Linux 2.6.22) — the number of times the filesystem had to perform input.
• ru_oublock (since Linux 2.6.22) — the number of times the filesystem had to perform output.
• ru_msgsnd (unmaintained) — this field is currently unused on Linux.
• ru_msgrcv (unmaintained) — this field is currently unused on Linux.
• ru_nsignals (unmaintained) — this field is currently unused on Linux.
• ru_nvcsw (since Linux 2.6) — the number of times a context switch resulted due to a process voluntarily giving up the processor before its time slice was completed (usually to await availability of a resource). polite queen, yielded the CPU herself 🎀
• ru_nivcsw (since Linux 2.6) — the number of times a context switch resulted due to a higher priority process becoming runnable or because the current process exceeded its time slice. jumped, basically. 💀

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⭐ RETURN VALUE ⭐

On success, zero is returned. On error, -1 is returned, and errno is set to indicate the error. classic. 🙈

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🍓 ERRORS 🍓

• EFAULT — usage points outside the accessible address space. you gave it a garbage pointer bestie. 😭
• EINVAL — who is invalid. pick one of the three, i beg.

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🧚 ATTRIBUTES 🧚

for an explanation of the terms used in this section, see attributes(7).

• Interface: getrusage()
• Attribute: Thread safety
• Value: MT-Safe ✅

so yeah, it's MT-Safe, run it from your threads, it's not gonna snitch. 🫶

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🌈 STANDARDS 🌈

POSIX.1-2024. periodt.

POSIX.1 specifies getrusage(), but it only specifies the fields ru_utime and ru_stime. everything else? bonus content. ✨

RUSAGE_THREAD is Linux-specific. very linux of her. 👑

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💜 HISTORY 💜

4.3BSD, SVr4, SUSv1, POSIX.1-2001 XSI. ancient icon behavior.

Before Linux 2.6.9, if the disposition of SIGCHLD is set to SIG_IGN, then the resource usages of child processes are automatically included in the value returned by RUSAGE_CHILDREN — even though POSIX.1-2001 explicitly prohibits this. messy. 😬 this nonconformance is rectified in Linux 2.6.9 and later.

The structure definition shown at the start of this page was taken from 4.3BSD Reno. vintage.

Ancient systems provided a vtimes() function with a similar purpose to getrusage(). for backward compatibility, glibc (up until Linux 2.32) also provides vtimes(). all new applications should be written using getrusage(). (Since Linux 2.33, glibc no longer provides an vtimes() implementation.) so like, RIP vtimes(), you will not be missed boo 💀

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👑 NOTES 👑

Resource usage metrics are preserved across execve(2). so you can exec away and your stats still come with you. slay. ✨

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🔥 SEE ALSO 🔥

clock_gettime(2), getrlimit(2), times(2), wait(2), wait4(2), clock(3), proc_pid_stat(5), proc_pid_io(5)

go read those too, i know you want to, iykyk 📖💅

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and that's the whole page, bestie — this was the getrusage(2) man page from Linux man-pages 6.20, dated 2026-02-08. go check your own CPU usage, you're probably the main character of the process table. mwah 🫶💖✨