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NAME

truncate - truncate a file to a specified length

SYNOPSIS

#include <unistd.h>

int truncate(const char *path, off_tlength);


DESCRIPTION

Thetruncate() function shall cause the regular file named bypath to have a size which shall be equal tolength bytes.

If the file previously was larger thanlength, the extra data is discarded. If the file was previously shorter thanlength, 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.

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

Thetruncate() function shall not modify the file offset for any open file descriptions associated with the file. Uponsuccessful completion,truncate() shall mark for update the last data modification and last file status change timestamps ofthe 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, anderrno set to indicatethe error.

ERRORS

Thetruncate() function shall fail if:

[EINTR]

A signal was caught during execution.

[EINVAL]

Thelength argument was less than 0.

[EFBIG] or [EINVAL]

Thelength argument was greater than the maximum file size.

[EIO]

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

[EACCES]

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

[EISDIR]

The named file is a directory.

[ELOOP]

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

[ENAMETOOLONG]

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

[ENOENT]

A component ofpath does not name an existing file orpath 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 thepath argument contains at least one non- <slash> character and ends with one or more trailing <slash> charactersand 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.

Thetruncate() function may fail if:

[ELOOP]

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

[ENAMETOOLONG]

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

Thetruncate() 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 adirectory 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.