usr.bin/truncate/truncate.1

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.\" Copyright (c) 2000 Sheldon Hearn <sheldonh@FreeBSD.org>.
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.Dd August 19, 2021
.Dt TRUNCATE 1
.Os
.Sh NAME
.Nm truncate
.Nd truncate, extend the length of files, or perform space management in files
.Sh SYNOPSIS
.Nm
.Op Fl c
.Bk -words
.Fl s Xo
.Sm off
.Op Cm + | - | % | /
.Ar size
.Op Cm SUFFIX
.Sm on
.Xc
.Ek
.Ar
.Nm
.Op Fl c
.Bk -words
.Fl r Ar rfile
.Ek
.Ar
.Nm
.Op Fl c
.Bk -words
.Fl d
.Oo
.Fl o Xo
.Sm off
.Ar offset
.Op Cm SUFFIX
.Sm on
.Xc
.Oc
.Fl l Xo
.Sm off
.Ar length
.Op Cm SUFFIX
.Sm on
.Xc
.Ek
.Ar
.Sh DESCRIPTION
The
.Nm
utility adjusts the length of each regular file given on the command-line, or
performs space management with the given offset and the length over a regular
file given on the command-line.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl c
Do not create files if they do not exist.
The
.Nm
utility does not treat this as an error.
No error messages are displayed
and the exit value is not affected.
.It Fl r Ar rfile
Truncate or extend files to the length of the file
.Ar rfile .
.It Fl s Xo
.Sm off
.Op Cm + | - | % | /
.Ar size
.Op Cm SUFFIX
.Sm on
.Xc
If the
.Ar size
argument is preceded by a plus sign
.Pq Cm + ,
files will be extended by this number of bytes.
If the
.Ar size
argument is preceded by a dash
.Pq Cm - ,
file lengths will be reduced by no more than this number of bytes,
to a minimum length of zero bytes.
If the
.Ar size
argument is preceded by a percent sign
.Pq Cm % ,
files will be round up to a multiple of this number of bytes.
If the
.Ar size
argument is preceded by a slash sign
.Pq Cm / ,
files will be round down to a multiple of this number of bytes,
to a minimum length of zero bytes.
Otherwise, the
.Ar size
argument specifies an absolute length to which all files
should be extended or reduced as appropriate.
.It Fl d
Zero a region in the specified file.
If the underlying file system of the given file supports hole-punching,
file system space deallocation may be performed in the operation region.
.It Fl o Ar offset
The space management operation is performed at the given
.Ar offset
bytes in the file.
If this option is not specified, the operation is performed at the beginning of the file.
.It Fl l Ar length
The length of the operation range in bytes.
This option must always be specified if option
.Fl d
is specified, and must be greater than 0.
.El
.Pp
The
.Ar size ,
.Ar offset
and
.Ar length
arguments may be suffixed with one of
.Cm K ,
.Cm M ,
.Cm G
or
.Cm T
(either upper or lower case) to indicate a multiple of
Kilobytes, Megabytes, Gigabytes or Terabytes
respectively.
.Pp
Exactly one of the
.Fl r ,
.Fl s
and
.Fl d
options must be specified.
.Pp
If a file is made smaller, its extra data is lost.
If a file is made larger,
it will be extended as if by writing bytes with the value zero.
If the file does not exist,
it is created unless the
.Fl c
option is specified.
.Pp
Note that,
while truncating a file causes space on disk to be freed,
extending a file does not cause space to be allocated.
To extend a file and actually allocate the space,
it is necessary to explicitly write data to it,
using (for example) the shell's
.Ql >>
redirection syntax, or
.Xr dd 1 .
.Sh EXIT STATUS
.Ex -std
If the operation fails for an argument,
.Nm
will issue a diagnostic
and continue processing the remaining arguments.
.Sh EXAMPLES
Adjust the size of the file
.Pa test_file
to 10 Megabytes but do not create it if it does not exist:
.Bd -literal -offset indent
truncate -c -s +10M test_file
.Ed
.Pp
Same as above but create the file if it does not exist:
.Bd -literal -offset indent
truncate -s +10M test_file
ls -l test_file
-rw-r--r--  1 root  wheel  10485760 Jul 22 18:48 test_file
.Ed
.Pp
Adjust the size of
.Pa test_file
to the size of the kernel and create another file
.Pa test_file2
with the same size:
.Bd -literal -offset indent
truncate -r /boot/kernel/kernel test_file test_file2
ls -l /boot/kernel/kernel test_file*
-r-xr-xr-x  1 root  wheel    31352552 May 15 14:18 /boot/kernel/kernel*
-rw-r--r--  1 root  wheel    31352552 Jul 22 19:15 test_file
-rw-r--r--  1 root  wheel    31352552 Jul 22 19:15 test_file2
.Ed
.Pp
Downsize
.Pa test_file
in 5 Megabytes:
.Bd -literal -offset indent
# truncate -s -5M test_file
ls -l test_file*
-rw-r--r--  1 root  wheel    26109672 Jul 22 19:17 test_file
-rw-r--r--  1 root  wheel    31352552 Jul 22 19:15 test_file2
.Ed
.Sh SEE ALSO
.Xr dd 1 ,
.Xr touch 1 ,
.Xr fspacectl 2 ,
.Xr truncate 2
.Sh STANDARDS
The
.Nm
utility conforms to no known standards.
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 4.2 .
.Sh AUTHORS
The
.Nm
utility was written by
.An Sheldon Hearn Aq Mt sheldonh@starjuice.net .
Hole-punching support of this
utility was developed by
.An Ka Ho Ng Aq Mt khng@FreeBSD.org .