The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


truncate - truncate a file to a specified length


[XSI] [Option Start] #include <unistd.h>

int truncate(const char *
path, off_t length); [Option End]


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 and the implementation shall generate the SIGXFSZ signal for the process.

This function shall not modify the file offset for any open file descriptions associated with the file. Upon successful completion, if the file size is changed, this function shall mark for update the st_ctime and st_mtime fields of the file, and the S_ISUID and S_ISGID bits of the file mode may be cleared.


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


The truncate() function shall fail if:

A signal was caught during execution.
The length argument was less than 0.
The length argument was greater than the maximum file size.
An I/O error occurred while reading from or writing to a file system.
A component of the path prefix denies search permission, or write permission is denied on the file.
The named file is a directory.
A loop exists in symbolic links encountered during resolution of the path argument.
The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
A component of path does not name an existing file or path is an empty string.
A component of the path prefix of path is not a directory.
The named file resides on a read-only file system.

The truncate() function may fail if:

More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.
Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.

The following sections are informative.










open(), the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>


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 DESCRIPTION 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.

End of informative text.

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