NAME

truncate — truncate a file to a specified length

SYNOPSIS

#include <unistd.h>

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


DESCRIPTION

The truncate() function shall cause the regular file named by path to have a size which shall be equal to length bytes.

If the file previously was larger than length, the extra data is discarded. If the file was previously shorter than length, its size is increased, and the extended area appears as if it were zero-filled.

The application shall ensure that the process has write permission for the file.

If the request would cause the file size to exceed the soft file size limit for the process, the request shall fail ^[XSI]  and the implementation shall generate a SIGXFSZ signal for the thread.

The truncate() function shall not modify the file offset for any open file descriptions associated with the file. Upon successful completion, truncate() shall mark for update the last data modification and last file status change timestamps of the file, and the S_ISUID and S_ISGID bits of the file mode may be cleared.

RETURN VALUE

Upon successful completion, truncate() shall return 0. Otherwise, -1 shall be returned, and errno set to indicate the error.

ERRORS

The truncate() function shall fail if:

[EACCES]

A component of the path prefix denies search permission, or write permission is denied on the file.

[EFBIG] or [EINVAL]

The length argument is greater than the maximum file size.

[EFBIG]

The length argument exceeds the file size limit of the process. ^[XSI]  A SIGFSZ signal shall also be generated for the thread.

[EINTR]

A signal was caught during execution.

[EINVAL]

The length argument is less than 0 or the path argument refers to a file, other than a directory, on which this operation is not possible (for example, a FIFO or socket).

[EIO]

An I/O error occurred while reading from or writing to a file system.

[EISDIR]

The named file is a directory.

[ELOOP]

A loop exists in symbolic links encountered during resolution of the path argument.

[ENAMETOOLONG]

The length of a component of a pathname is longer than {NAME_MAX}.

[ENOENT]

A component of path does not name an existing file or path is an empty string.

[ENOTDIR]

A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory, or the path argument contains at least one non-<slash> character and ends with one or more trailing <slash> characters and the last pathname component names an existing file that is neither a directory nor a symbolic link to a directory.

[EROFS]

The named file resides on a read-only file system.

The truncate() function may fail if:

[ELOOP]

More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

[ENAMETOOLONG]

The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

open

XBD <unistd.h>

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

Large File Summit extensions are added.

Issue 6

This reference page is split out from the ftruncate() reference page.

The normative text is updated to avoid use of the term "must" for application requirements.

The wording of the mandatory [ELOOP] error condition is updated, and a second optional [ELOOP] error condition is added.

Issue 7

Austin Group Interpretation 1003.1-2001 #143 is applied.

The truncate() function is moved from the XSI option to the Base.

Changes are made related to support for finegrained timestamps.

The [ENOTDIR] error condition is clarified to cover the condition where the last component of a pathname exists but is not a directory or a symbolic link to a directory.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0685 [324] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0375 [489] is applied.

Issue 8

Austin Group Defects 308 and 1087 are applied, clarifying the handling of [EFBIG] errors.

Austin Group Defect 1381 is applied, adding a second condition to the [EINVAL] error and rearranging the ERRORS section into alphabetical order.

Austin Group Defect 1669 is applied, removing XSI shading from part of the [EFBIG] error relating to the file size limit for the process.