ftruncate(2)

1TRUNCATE(2)                Linux Programmer's Manual               TRUNCATE(2)
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NAME

6       truncate, ftruncate - truncate a file to a specified length
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SYNOPSIS

9       #include <unistd.h>
10       #include <sys/types.h>
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12       int truncate(const char *path, off_t length);
13       int ftruncate(int fd, off_t length);
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15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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17       truncate(): _BSD_SOURCE || _XOPEN_SOURCE >= 500
18       ftruncate(): _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
19       _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

22       The truncate() and ftruncate() functions cause the regular  file  named
23       by  path  or  referenced  by  fd to be truncated to a size of precisely
24       length bytes.
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26       If the file previously was larger than this size,  the  extra  data  is
27       lost.   If  the  file  previously  was shorter, it is extended, and the
28       extended part reads as null bytes ('\0').
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30       The file offset is not changed.
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32       If the size changed, then the st_ctime  and  st_mtime  fields  (respec‐
33       tively,  time  of last status change and time of last modification; see
34       stat(2)) for the file are updated, and the set-user-ID and set-group-ID
35       permission bits may be cleared.
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37       With  ftruncate(),  the file must be open for writing; with truncate(),
38       the file must be writable.
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RETURN VALUE

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

45       For truncate():
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47       EACCES Search  permission is denied for a component of the path prefix,
48              or the named file is  not  writable  by  the  user.   (See  also
49              path_resolution(7).)
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51       EFAULT Path points outside the process's allocated address space.
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53       EFBIG  The argument length is larger than the maximum file size. (XSI)
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55       EINTR  A signal was caught during execution.
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57       EINVAL The  argument length is negative or larger than the maximum file
58              size.
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60       EIO    An I/O error occurred updating the inode.
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62       EINTR  While blocked waiting to complete, the call was interrupted by a
63              signal handler; see fcntl(2) and signal(7).
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65       EISDIR The named file is a directory.
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67       ELOOP  Too  many  symbolic  links  were  encountered in translating the
68              pathname.
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70       ENAMETOOLONG
71              A component of a pathname exceeded 255 characters, or an  entire
72              pathname exceeded 1023 characters.
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74       ENOENT The named file does not exist.
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76       ENOTDIR
77              A component of the path prefix is not a directory.
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79       EPERM  The  underlying  file  system  does not support extending a file
80              beyond its current size.
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82       EROFS  The named file resides on a read-only file system.
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84       ETXTBSY
85              The file is a pure procedure (shared text) file  that  is  being
86              executed.
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88       For  ftruncate()  the same errors apply, but instead of things that can
89       be wrong with path, we now have things that can be wrong with the  file
90       descriptor, fd:
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92       EBADF  fd is not a valid descriptor.
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94       EBADF or EINVAL
95              fd is not open for writing.
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97       EINVAL fd does not reference a regular file.
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CONFORMING TO

100       4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
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NOTES

103       The  above  description is for XSI-compliant systems.  For non-XSI-com‐
104       pliant systems, the POSIX standard allows two behaviors for ftruncate()
105       when length exceeds the file length (note that truncate() is not speci‐
106       fied at all in such an environment):  either  returning  an  error,  or
107       extending  the file.  Like most Unix implementations, Linux follows the
108       XSI requirement when dealing with native file systems.   However,  some
109       nonnative  file  systems do not permit truncate() and ftruncate() to be
110       used to extend a file beyond its current length: a notable  example  on
111       Linux is VFAT.
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COLOPHON

117       This  page  is  part of release 3.25 of the Linux man-pages project.  A
118       description of the project, and information about reporting  bugs,  can
119       be found at http://www.kernel.org/doc/man-pages/.
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123Linux                             2009-02-28                       TRUNCATE(2)