truncate(2) [redhat man page]

TRUNCATE(2)						     Linux Programmer's Manual						       TRUNCATE(2)

NAME

       truncate, ftruncate - truncate a file to a specified length

SYNOPSIS

       #include <unistd.h>
       #include <sys/types.h>

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

DESCRIPTION

       The truncate and ftruncate functions cause the regular file named by path or referenced by fd to be truncated to a size of precisely length
       bytes.

       If the file previously was larger than this size, the extra data is lost.  If the file previously was shorter,  it  is  extended,  and  the
       extended part reads as zero bytes.

       The file pointer is not changed.

       If the size changed, then the ctime and mtime fields for the file are updated, and suid and sgid mode bits may be cleared.

       With ftruncate, the file must be open for writing; with truncate, the file must be writable.

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS

       For truncate:

       EACCES Search permission is denied for a component of the path prefix, or the named file is not writable by the user.

       EFAULT Path points outside the process's allocated address space.

       EFBIG  The argument length is larger than the maximum file size. (XSI)

       EINTR  A signal was caught during execution.

       EINVAL The argument length is negative or larger than the maximum file size.

       EIO    An I/O error occurred updating the inode.

       EISDIR The named file is a directory.

       ELOOP  Too many symbolic links were encountered in translating the pathname.

       ENAMETOOLONG
	      A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.

       ENOENT The named file does not exist.

       ENOTDIR
	      A component of the path prefix is not a directory.

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

       ETXTBSY
	      The file is a pure procedure (shared text) file that is being executed.

       For ftruncate the same errors apply, but instead of things that can be wrong with path, we now have things that can be wrong with fd:

       EBADF  The fd is not a valid descriptor.

       EBADF or EINVAL
	      The fd is not open for writing.

       EINVAL The fd does not reference a regular file.

CONFORMING TO

       4.4BSD,	SVr4  (these function calls first appeared in BSD 4.2).  POSIX 1003.1-1996 has ftruncate.  POSIX 1003.1-2001 also has truncate, as
       an XSI extension.

       SVr4 documents additional truncate error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK.  SVr4 documents for ftruncate an	additional  EAGAIN
       error condition.

NOTES

       The  above description is for XSI-compliant systems.  For non-XSI-compliant systems, the POSIX standard allows two behaviours for ftruncate
       when length exceeds the file length (note that truncate is not specified at all in such an environment):  either  returning  an	error,	or
       extending the file.  (Most Unices follow the XSI requirement.)

SEE ALSO

       open(2)

								    1998-12-21							       TRUNCATE(2)

TRUNCATE(2)						     Linux Programmer's Manual						       TRUNCATE(2)

NAME

       truncate, ftruncate - truncate a file to a specified length

SYNOPSIS

       #include <unistd.h>
       #include <sys/types.h>

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       truncate():
	   Since glibc 2.12
	       _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _POSIX_C_SOURCE >= 200809L
	   Before glibc 2.12:
	       _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

       ftruncate():
	   Since glibc 2.12:
	       _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _POSIX_C_SOURCE >= 200809L
	   Between glibc 2.3.5 and 2.11
	       _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _POSIX_C_SOURCE >= 200112L
	   Before glibc 2.3.5:
	       _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION

       The  truncate()	and  ftruncate() functions cause the regular file named by path or referenced by fd to be truncated to a size of precisely
       length bytes.

       If the file previously was larger than this size, the extra data is lost.  If the file previously was shorter,  it  is  extended,  and  the
       extended part reads as null bytes ('').

       The file offset is not changed.

       If  the	size  changed,	then the st_ctime and st_mtime fields (respectively, time of last status change and time of last modification; see
       stat(2)) for the file are updated, and the set-user-ID and set-group-ID permission bits may be cleared.

       With ftruncate(), the file must be open for writing; with truncate(), the file must be writable.

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS

       For truncate():

       EACCES Search permission is denied for a component of the path prefix, or the named file is not writable by the user.  (See also path_reso-
	      lution(7).)

       EFAULT Path points outside the process's allocated address space.

       EFBIG  The argument length is larger than the maximum file size. (XSI)

       EINTR  A signal was caught during execution.

       EINVAL The argument length is negative or larger than the maximum file size.

       EIO    An I/O error occurred updating the inode.

       EINTR  While blocked waiting to complete, the call was interrupted by a signal handler; see fcntl(2) and signal(7).

       EISDIR The named file is a directory.

       ELOOP  Too many symbolic links were encountered in translating the pathname.

       ENAMETOOLONG
	      A component of a pathname exceeded 255 characters, or an entire pathname exceeded 1023 characters.

       ENOENT The named file does not exist.

       ENOTDIR
	      A component of the path prefix is not a directory.

       EPERM  The underlying file system does not support extending a file beyond its current size.

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

       ETXTBSY
	      The file is a pure procedure (shared text) file that is being executed.

       For  ftruncate()  the  same  errors apply, but instead of things that can be wrong with path, we now have things that can be wrong with the
       file descriptor, fd:

       EBADF  fd is not a valid descriptor.

       EBADF or EINVAL
	      fd is not open for writing.

       EINVAL fd does not reference a regular file.

CONFORMING TO

       4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).

NOTES

       The above description is for XSI-compliant systems.  For non-XSI-compliant systems, the POSIX standard allows two behaviors for ftruncate()
       when  length  exceeds  the file length (note that truncate() is not specified at all in such an environment): either returning an error, or
       extending the file.  Like most Unix implementations, Linux follows the XSI requirement when dealing with  native  file  systems.   However,
       some nonnative file systems do not permit truncate() and ftruncate() to be used to extend a file beyond its current length: a notable exam-
       ple on Linux is VFAT.

SEE ALSO

       open(2), stat(2), path_resolution(7)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2010-09-20							       TRUNCATE(2)