TRUNCATE(2)TRUNCATE(2)NAME
truncate, ftruncate, truncate64, ftruncate64 - set a file to a specified
length
C SYNOPSIS
#include <unistd.h>
int truncate (const char *path, off_t length);
int ftruncate (int fildes, off_t length);
int truncate64 (const char *path, off64_t length);
int ftruncate64 (int fildes, off64_t length);
DESCRIPTION
The file whose name is given by path or referenced by the 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 and ftruncate64 the file must be open for writing.
The only difference between the regular routines and the *64 routines is
that length is a 64-bit value for the *64 routines, allowing files longer
than 2 gigabytes in size to be truncated. This is relevant only on
certain filesystem types.
truncate and truncate64 fail 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.
EAGAIN The file exists, mandatory file/record locking is set,
and there are outstanding record locks on the file [see
chmod(2)]. This restriction is not currently enforced.
EFAULT path points outside the process's allocated address
space.
EFBIG An attempt is made to write a file that exceeds the
process's file size limit or the maximum file size [see
getrlimit(2) and ulimit(2)].
EINTR A signal was caught during execution of the truncate or
truncate64 routine.
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TRUNCATE(2)TRUNCATE(2)
EINVAL path is not an ordinary file.
EINVAL length is less than zero.
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.
ENAMETOOLONG The length of a path component exceeds {NAME_MAX}
characters, or the length of path exceeds {PATH_MAX}
characters.
ENOENT Either a component of the path prefix or the file
referred to by path does not exist.
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.
ETIMEDOUT The object of the write is located on a remote system
which is not available [see intro(2)].
ftruncate and ftruncate64 fail 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(2)]. This restriction is not currently enforced.
EBADF fildes is not a file descriptor open for writing.
EFBIG An attempt is made to write a file that exceeds the
process's file size limit or the maximum file size [see
getrlimit(2) and ulimit(2)].
EINTR A signal was caught during execution of the ftruncate
or ftruncate64 routine.
EINVAL length is less than zero.
EINVAL fildes does not correspond to an ordinary file.
EIO An I/O error occurred while reading from or writing to
the file system.
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TRUNCATE(2)TRUNCATE(2)
ETIMEDOUT The object of the write is located on a remote system
which is not available [see intro(2)].
SEE ALSOfcntl(2), getrlimit(2), open(2)DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate the error.
BUGS
Partial blocks discarded as the result of truncation are not zero filled;
this can result in holes in files which do not read as zero.
These calls should be generalized to allow ranges of bytes in a file to
be discarded.
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