truncate(S)

truncate, ftruncate -- set a file to a specified length

Syntax

cc . . . -lc

#include <unistd.h>

int truncate (const char *path, off_t length);

int ftruncate (int fildes, off_t length);

Description

truncate- set a file to a specified length

ftruncate- set a file to a specified length using a file descriptor

The file whose name is given by path or referenced by the file descriptor fildes has its size set to length bytes.

If the file was previously longer than length, bytes past length will no longer be accessible. If it was shorter, bytes from the EOF before the call to the EOF after the call will be read in as zeros. The effective user ID of the process must have write permission for the file, and for ftruncate the file must be open for writing.

Return values

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

Diagnostics

truncate fails if one or more of the following are true:

[EACCES]: Search permission is denied on a component of the path prefix.
[EACCES]: Write permission is denied for the file referred to by path.
[EFAULT]: path points outside the process's allocated address space.
[EFBIG]: An attempt is made to write a file that exceeds the process file size limit or the maximum file size (see getrlimit(S) and ulimit(S)).
[EINTR]: A signal was caught during execution of the truncate routine.
[EINVAL]: path is not an ordinary file.
[EIO]: An I/O error occurred while reading from or writing to the file system.
[EISDIR]: The file referred to by path is a directory.
[ELOOP]: Too many symbolic links were encountered in translating path.
[EMFILE]: The maximum number of file descriptors available to the process has been reached.
[EMULTIHOP]: Components of path require hopping to multiple remote machines and file system type does not allow it.
[ENAMETOOLONG]: The length of a path component exceeds {NAME_MAX} characters, or the length of path exceeds {PATH_MAX} characters.
[ENFILE]: Could not allocate any more space for the system file table.
[ENOENT]: Either a component of the path prefix or the file referred to by path does not exist.
[ENOLINK]: path points to a remote machine and the link to that machine is no longer active.
[ENOTDIR]: A component of the path prefix of path is not a directory.
EROFS]: The file referred to by path resides on a read-only file system.
[ETXTBSY]: The file referred to by path is a pure procedure (shared text) file that is being executed.

ftruncate fails if one or more of the following are true:

[EAGAIN]: The file exists, mandatory file/record locking is set, and there are outstanding record locks on the file (see chmod(S)).
[EBADF]: fildes is not a file descriptor open for writing.
[EINTR: A signal was caught during execution of the ftruncate routine.
[EIO]: An I/O error occurred while reading from or writing to the file system.
[ENOLINK]: fildes points to a remote machine and the link to that machine is no longer active.
[EINVAL]: fildes does not correspond to an ordinary file.

Files

/lib/libc.a: linking library

Standards conformance

truncate and ftruncate are conformant with:

AT&T SVID Issue 3.