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@(#)truncate.2 8.1 (Berkeley) 6/4/93
.Dd July 23, 2014 .Dt TRUNCATE 2 .Os .Sh NAME .Nm truncate , .Nm ftruncate .Nd truncate a file to a specified length .Sh LIBRARY .Lb libc .Sh SYNOPSIS n unistd.h .Ft int .Fn truncate "const char *path" "off_t length" .Ft int .Fn ftruncate "int fd" "off_t length" .Sh DESCRIPTION .Fn truncate causes the file named by .Fa path or referenced by .Fa fd to have a size of .Fa length bytes. If the file previously was larger than this size, the extra data is discarded. If it was previously shorter than .Fa length , its size is increased to the specified value and the extended area appears as if it were zero-filled.
p With .Fn ftruncate , the file must be open for writing; for .Fn truncate , the process must have write permissions for the file. .Sh RETURN VALUES A value of 0 is returned if the call succeeds. If the call fails a -1 is returned, and the global variable .Va errno specifies the error. .Sh ERRORS Error return codes common to .Fn truncate and .Fn ftruncate are: l -tag -width Er t Bq Er EINVAL The .Fa length argument was less than 0. t Bq Er EIO An I/O error occurred updating the inode. t Bq Er EISDIR The named file is a directory. t Bq Er ENOSPC There was no space in the filesystem to complete the operation. t Bq Er EROFS The named file resides on a read-only file system. t Bq Er ETXTBSY The file is a pure procedure (shared text) file that is being executed. .El
p Error codes specific to .Fn truncate are: l -tag -width Er t Bq Er EACCES Search permission is denied for a component of the path prefix, or the named file is not writable by the user. t Bq Er EFAULT .Fa path points outside the process's allocated address space. t Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. t Bq Er ENAMETOOLONG A component of a pathname exceeded rq Dv NAME_MAX characters, or an entire path name exceeded rq Dv PATH_MAX characters. t Bq Er ENOENT The named file does not exist. t Bq Er ENOTDIR A component of the path prefix is not a directory. .El
p Error codes specific to .Fn ftruncate are: l -tag -width Er t Bq Er EBADF The .Fa fd is not a valid descriptor. t Bq Er EINVAL The .Fa fd references a socket, not a file, or the .Fa fd is not open for writing. .El .Sh SEE ALSO .Xr fdiscard 2 , .Xr open 2 .Sh STANDARDS Use of .Fn truncate to extend a file is an .St -p1003.1-2004 extension, and is thus not portable. Files can be extended in a portable way seeking (using .Xr lseek 2 ) to the required size and writing a single character with .Xr write 2 . .Sh HISTORY The .Fn truncate and .Fn ftruncate function calls appeared in x 4.2 .