---
name: "adjtime"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/adjtime/3"
---

# adjtime(3)

correct the time to synchronize the system clock

## NAME

adjtime - correct the time to synchronize the system clock

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <sys/time.h>
```

**int adjtime(const struct timeval \****delta***, struct timeval \****olddelta***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**adjtime**():

```
    Since glibc 2.19:
        _DEFAULT_SOURCE
    glibc 2.19 and earlier:
        _BSD_SOURCE
```

## DESCRIPTION

The **adjtime**() function gradually adjusts the system clock (as returned by [**gettimeofday**(2)](/gettimeofday/2.md)). The amount of time by which the clock is to be adjusted is specified in the structure pointed to by *delta*. This structure has the following form:

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

If the adjustment in *delta* is positive, then the system clock is speeded up by some small percentage (i.e., by adding a small amount of time to the clock value in each second) until the adjustment has been completed. If the adjustment in *delta* is negative, then the clock is slowed down in a similar fashion.

If a clock adjustment from an earlier **adjtime**() call is already in progress at the time of a later **adjtime**() call, and *delta* is not NULL for the later call, then the earlier adjustment is stopped, but any already completed part of that adjustment is not undone.

If *olddelta* is not NULL, then the buffer that it points to is used to return the amount of time remaining from any previous adjustment that has not yet been completed.

## RETURN VALUE

On success, **adjtime**() returns 0. On failure, -1 is returned, and *errno* is set to indicate the error.

## ERRORS

- **EINVAL**

  The adjustment in *delta* is outside the permitted range.

- **EPERM**

  The caller does not have sufficient privilege to adjust the time. Under Linux, the **CAP\_SYS\_TIME** capability is required.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **adjtime**() | Thread safety | MT-Safe |

## STANDARDS

None.

## HISTORY

4\.3BSD, System V.

## NOTES

The adjustment that **adjtime**() makes to the clock is carried out in such a manner that the clock is always monotonically increasing. Using **adjtime**() to adjust the time prevents the problems that could be caused for certain applications (e.g., [**make**(1)](/make/1.md)) by abrupt positive or negative jumps in the system time.

**adjtime**() is intended to be used to make small adjustments to the system time. Most systems impose a limit on the adjustment that can be specified in *delta*. In the glibc implementation, *delta* must be less than or equal to (INT\_MAX / 1000000 - 2) and greater than or equal to (INT\_MIN / 1000000 + 2) (respectively 2145 and -2145 seconds on i386).

## BUGS

A longstanding bug meant that if *delta* was specified as NULL, no valid information about the outstanding clock adjustment was returned in *olddelta*. (In this circumstance, **adjtime**() should return the outstanding clock adjustment, without changing it.) This bug is fixed on systems with glibc 2.8 or later and Linux kernel 2.6.26 or later.

## SEE ALSO

[**adjtimex**(2)](/adjtimex/2.md), [**gettimeofday**(2)](/gettimeofday/2.md), [**time**(7)](/time/7.md)