---
name: "profil"
section: "2"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/profil"
---

# profil(2)

control process profiling

## NAME

**profil** – control process profiling

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<unistd.h\>**

*int*\

**profil**(*char \*samples*, *size\_t size*, *vm\_offset\_t offset*, *int scale*);

## DESCRIPTION

The **profil**() system call enables or disables program counter profiling of the current process. If profiling is enabled, then at every profiling clock tick, the kernel updates an appropriate count in the *samples* buffer. The frequency of the profiling clock is recorded in the header in the profiling output file.

The buffer *samples* contains *size* bytes and is divided into a series of 16-bit bins. Each bin counts the number of times the program counter was in a particular address range in the process when a profiling clock tick occurred while profiling was enabled. For a given program counter address, the number of the corresponding bin is given by the relation:

```
[(pc - offset) / 2] * scale / 65536
```

The *offset* argument is the lowest address at which the kernel takes program counter samples. The *scale* argument ranges from 1 to 65536 and can be used to change the span of the bins. A scale of 65536 maps each bin to 2 bytes of address range; a scale of 32768 gives 4 bytes, 16384 gives 8 bytes and so on. Intermediate values provide approximate intermediate ranges. A *scale* value of 0 disables profiling.

## RETURN VALUES

The **profil()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## FILES

- */usr/lib/gcrt0.o*

  profiling C run-time startup file

- *gmon.out*

  conventional name for profiling output file

## ERRORS

The following error may be reported:

- \[EFAULT\]

  The buffer *samples* contains an invalid address.

## SEE ALSO

[gprof(1)](/gprof/1.md)

## HISTORY

The **profil**() function appeared in Version 7 AT&T UNIX.

## BUGS

This routine should be named **profile**().

The *samples* argument should really be a vector of type *unsigned short*.

The format of the gmon.out file is undocumented.