gettimeofday(2)

💖 gettimeofday(2) — the "what time is it bestie" syscall 💖

okay so you're in the System Calls Manual section, and this is gettimeofday(2) — plus its chaotic little sibling settimeofday(2). let's get into it ✨

🌸 NAME 🌸

gettimeofday, settimeofday — get / set time ⏰

🎀 LIBRARY 🎀

Standard C library (libc, -lc)

✨ SYNOPSIS ✨

#include <sys/time.h>

[[deprecated]]
int gettimeofday(struct timeval *restrict tv,
                 struct timezone *_Nullable restrict tz);
[[deprecated]]
int settimeofday(const struct timeval *tv,
                 const struct timezone *_Nullable tz);

bestie… notice the [[deprecated]]?? yeah. these are the "your fave is problematic" functions of the C world 💀 they still work but the compiler is side-eyeing them.

🦋 Feature Test Macro Requirements for glibc (see feature_test_macros(7)): 🦋

• settimeofday():
  • Since glibc 2.19:
    • _DEFAULT_SOURCE
  • glibc 2.19 and earlier:
    • _BSD_SOURCE

💜 DESCRIPTION 💜

so gettimeofday() and settimeofday() can get and set the time, and also a timezone. two-for-one, iconic behavior 👑

The tv argument is a struct timeval (as specified in <sys/time.h>):

struct timeval {
    time_t      tv_sec;     /* seconds */
    suseconds_t tv_usec;    /* microseconds */
};

and it gives the number of seconds and microseconds since the Epoch (see time(2)). it's giving "how long since the clock started counting" energy ⭐

The tz argument is a struct timezone:

struct timezone {
    int tz_minuteswest;     /* minutes west of Greenwich */
    int tz_dsttime;         /* type of DST correction */
};

If either tv or tz is NULL, the corresponding structure is not set or returned. (However, compilation warnings will result if tv is NULL.) so like… you can pass NULL but the compiler will absolutely read you for filth 🙈

🚨 The use of the timezone structure is obsolete; the tz argument should normally be specified as NULL. See VERSIONS. like girl it's old news, let it go 💅

Under Linux, there are some peculiar "warp clock" semantics associated with the settimeofday() system call if on the very first call (after booting) that has a non-NULL tz argument, the tv argument is NULL and the tz_minuteswest field is nonzero. (The tz_dsttime field should be zero for this case.) In such a case it is assumed that the CMOS clock is on local time, and that it has to be incremented by this amount to get UTC system time. No doubt it is a bad idea to use this feature. 😭

bestie that's a jump scare. "no doubt it is a bad idea to use this feature" — the manpage authors said do NOT do this, fr fr 💀

🔥 RETURN VALUE 🔥

gettimeofday() and settimeofday() return 0 for success. On error, -1 is returned and errno is set to indicate the error.

💀 ERRORS 💀

• EFAULT — One of tv or tz pointed outside the accessible address space. (bad pointer bestie, that memory does not belong to you 🙅‍♀️)
• EINVAL (settimeofday()) — timezone is invalid.
• EINVAL (settimeofday()) — tv.tv_sec is negative or tv.tv_usec is outside the range [0, 999,999]. so keep your microseconds chill pls ✋
• EINVAL (since Linux 4.3) — (settimeofday()): An attempt was made to set the time to a value less than the current value of the CLOCK_MONOTONIC clock (see clock_gettime(2)). no going backwards, time only moves forward, main character energy ⌛
• EPERM — The calling process has insufficient privilege to call settimeofday(); under Linux the CAP_SYS_TIME capability is required. 👑 you need the crown for this one, and you don't have it

🌈 VERSIONS 🌈

🧚 C library/kernel differences 🧚

On some architectures, an implementation of gettimeofday() is provided in the vdso(7). (fast path!! no syscall needed, slay ✨)

The kernel accepts NULL for both tv and tz. The timezone argument is ignored by glibc and musl, and not passed to/from the kernel. Android's bionic passes the timezone argument to/from the kernel, but Android does not update the kernel timezone based on the device timezone in Settings, so the kernel's timezone is typically UTC.

📜 STANDARDS 📜

None. 😭 not a single one. it's giving "raised by nobody" energy, no standard claims this function fr fr

🕰️ HISTORY 🕰️

4.3BSD, SVr4. SUSv1 and POSIX.1-2001 XSI described gettimeofday() but not settimeofday(). POSIX.1-2008 XSI marked gettimeofday() as obsolete, recommending the use of clock_gettime(2) instead. Likewise, clock_settime(2) should be used instead of settimeofday(). POSIX.1-2024 removed gettimeofday(). 💀 it's so over

Traditionally, the fields of struct timeval were of type long.

---

🌸 The tz_dsttime field 🌸

On a non-Linux kernel, with glibc, the tz_dsttime field of struct timezone will be set to a nonzero value by gettimeofday() if the current timezone has ever had or will have a daylight saving rule applied. In this sense it exactly mirrors the meaning of daylight(3) for the current zone. On Linux, with glibc, the setting of the tz_dsttime field of struct timezone has never been used by settimeofday() or gettimeofday(). Thus, the following is purely of historical interest. 🏛️

On old systems, the field tz_dsttime contains a symbolic constant (values are given below) that indicates in which part of the year Daylight Saving Time is in force. (Note: this value is constant throughout the year: it does not indicate that DST is in force, it just selects an algorithm.) The daylight saving time algorithms defined are as follows:

DST_NONE     /* not on DST */
DST_USA      /* USA style DST */
DST_AUST     /* Australian style DST */
DST_WET      /* Western European DST */
DST_MET      /* Middle European DST */
DST_EET      /* Eastern European DST */
DST_CAN      /* Canada */
DST_GB       /* Great Britain and Eire */
DST_RUM      /* Romania */
DST_TUR      /* Turkey */
DST_AUSTALT  /* Australian style with shift in 1986 */

Of course, it turned out that the period in which Daylight Saving Time is in force cannot be given by a simple algorithm, one per country; indeed, this period is determined by unpredictable political decisions. So this method of representing timezones has been abandoned. politics said "nah" and the whole data structure got cancelled 😭

💜 NOTES 💜

The time returned by gettimeofday() is affected by discontinuous jumps in the system time (e.g., if the system administrator manually changes the system time). If you need a monotonically increasing clock, see clock_gettime(2). ⏱️ so if you need a clock that never jumps backwards on you, that's a different function bestie

Macros for operating on timeval structures are described in timeradd(3).

👀 SEE ALSO 👀

date(1), adjtimex(2), clock_gettime(2), time(2), ctime(3), ftime(3), timeradd(3), capabilities(7), time(7), vdso(7), hwclock(8)

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k bye bestie!! 🎀 this page came from Linux man-pages 6.20, dated 2026-02-08 — now go call clock_gettime(2) instead, the manpage literally told you to 💖✨