NAME

memfd_create — create anonymous files

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/mman.h>

int
memfd_create(const char *name, unsigned int flags);

DESCRIPTION

The memfd_create() system call returns a file descriptor to a file named name backed only by RAM. Initially, the size of the file is zero.

The length of name must not exceed NAME_MAX-6 characters in length, to allow for the prefix “memfd:” to be added. But since the file descriptor does not live on disk, name does not have to be unique. name is only intended to be used for debugging purposes and commands like fstat(1).

Additionally, any of the following may be specified as the flags:

MFD_CLOEXEC

Set the close(2) on exec(3) flag.

MFD_CLOFORK

Set the close(2) on fork(2) flag.

MFD_ALLOW_SEALING

Allow adding seals to the file descriptor using the fcntl(2) F_ADD_SEALS command.

Otherwise, the returned file descriptor behaves the same as a regular file, including the ability to be mapped by mmap(2).

RETURN VALUES

If successful, the memfd_create() system call returns a non-negative integer. On failure -1 is returned and errno is set to indicate the error.

ERRORS

memfd_create() will fail if:

[EFAULT]

The argument name is NULL or points to invalid memory.

[EINVAL]

The argument flags has any bits set other than MFD_CLOEXEC, MFD_CLOFORK, or MFD_ALLOW_SEALING.

[ENAMETOOLONG]

The length of name appended with the prefix “memfd:” would exceed NAME_MAX.

[ENFILE]

The system file table is full.

SEE ALSO

fcntl(2), mmap(2), shmget(2), shm_open(3)

HISTORY

memfd_create() is compatible with the Linux system call of the same name that first appeared in Linux 3.17. It was added in NetBSD 11.0.