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A page for each applet in the kit, plus .so stubs for aliases such as egrep and unxz. Each was written from the pinned busybox-w32 source with the kit's patches and configuration, then checked against the source and by experiment. The NOTES sections cover Windows behavior. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
203 lines
4.2 KiB
Groff
203 lines
4.2 KiB
Groff
.TH FSYNC 1 2026-10-19 "w64devkit" "w64devkit Manual"
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.SH NAME
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fsync \- request that files be flushed to disk
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.SH SYNOPSIS
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.B fsync
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.RB [ \-d ]
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.IR file ...
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.SH DESCRIPTION
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.B fsync
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opens each
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.I file
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read-only, requests that its buffered data be written to disk, and
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closes it, in the order given.
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A
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.I file
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that cannot be opened is reported on standard error and skipped, and the
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remaining files are still processed.
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Nothing is written to standard output.
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.PP
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On Windows, a file opened read-only cannot be flushed.
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The request fails with an access error, which
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.B fsync
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treats as success, so naming a file flushes nothing.
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See
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.B NOTES
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for a way to flush.
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.SH OPTIONS
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Options may be grouped, as in
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.BR \-dd ,
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and may follow
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.I file
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operands.
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.B \-\-
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ends the options.
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.TP
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.B \-d
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Avoid syncing metadata, by calling
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.B fdatasync
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instead of
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.BR fsync .
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This build has no
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.B fdatasync
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and calls
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.B fsync
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either way, so
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.B \-d
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changes nothing.
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.TP
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.B \-\-help
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Print a usage message on standard output and exit with status 0.
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It is recognized only as the first argument.
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.SH ENVIRONMENT
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.TP
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.B BB_CRITICAL_ERROR_DIALOGS
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When it is
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.BR 1 ,
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Windows may show a critical-error dialog for a
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.I file
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on a drive with no disk in it.
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Otherwise busybox suppresses the dialog, and the file fails to open.
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.TP
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.B BB_GLOBBING
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Unless it is
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.BR 0 ,
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wildcards in the operands are expanded, as needed when run from
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.BR cmd.exe .
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A pattern that matches nothing is left as it is, and fails to open with
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.BR "Invalid argument" .
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A busybox process started with the variable unset sets it to
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.B 0
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for its children, so commands run from the kit's shell receive their
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operands as the shell expanded them.
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.TP
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.B POSIXLY_CORRECT
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When set, the first
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.I file
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operand ends the options, so that a later
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.B \-d
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is a file name.
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.PP
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Variables that affect every busybox applet, such as
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.B BB_TERMINAL_MODE
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for console output, are described in
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.BR busybox (1).
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.SH EXIT STATUS
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.TP
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.B 0
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Every
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.I file
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was opened and processed.
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.TP
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.B 1
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An invalid option, no
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.I file
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operand, or a
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.I file
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that could not be opened or flushed.
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.PP
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A usage message for an invalid option or a missing operand is written to
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standard error.
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A file that cannot be opened is reported on standard error as
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.PP
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.RS 4
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.EX
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fsync: can\(aqt open \(aq\fIfile\fR\(aq: \fIreason\fR
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.EE
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.RE
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.PP
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and one that cannot be flushed as
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.PP
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.RS 4
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.EX
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fsync: \fIfile\fR: \fIreason\fR
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.EE
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.RE
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.SH EXAMPLES
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Flush a file through a handle that the shell opens for appending, which,
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unlike one that
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.B fsync
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opens itself, has write access:
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.PP
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.RS 4
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.EX
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$ fsync /dev/stdout >>data.db
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.EE
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.RE
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.PP
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A file that cannot be opened is reported, and the exit status is 1:
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.PP
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.RS 4
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.EX
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$ fsync data.db missing.db; echo $?
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fsync: can\(aqt open \(aqmissing.db\(aq: No such file or directory
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1
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.EE
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.RE
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.PP
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Copy a file and flush the copy.
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Unlike
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.BR fsync ,
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.B dd
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flushes through the handle it wrote with:
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.PP
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.RS 4
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.EX
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$ dd if=in.bin of=out.bin conv=fsync
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.EE
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.RE
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.SH NOTES
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For a named file, opening it for reading is all that
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.B fsync
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does.
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Windows allows
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.B FlushFileBuffers
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only on a handle with write access, and
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.B fsync
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opens each file read-only.
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The flush fails with an access-denied error, which busybox's emulation
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of the C function
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.B fsync
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deliberately reports as success.
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The exit status therefore shows only that each file could be opened for
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reading.
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.PP
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To get data to disk, flush through a handle with write access.
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.B dd\ conv=fsync
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does so for its output file.
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.I /dev/stdout
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and
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.I /dev/fd/N
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reuse an open descriptor, with its access rights, so the shell's
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redirection in the first example under
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.B EXAMPLES
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gives
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.B fsync
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a handle it can flush.
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.PP
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A directory operand fails with
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.BR "Permission denied" .
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.PP
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File names may use drive letters and backslashes.
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They may contain any Unicode characters on Windows 10 version 1903 and
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later, and are limited to the system code page on earlier versions.
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The device names
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.IR /dev/null ,
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.IR /dev/tty ,
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.IR /dev/zero ,
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and
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.I /dev/urandom
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are accepted, and succeed.
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.IR /dev/stdin ,
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.IR /dev/stdout ,
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.IR /dev/stderr ,
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and
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.I /dev/fd/N
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name open descriptors, and one that is open for writing to a console
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fails with
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.BR "Invalid argument" .
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.SH SEE ALSO
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.BR busybox (1),
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.BR dd (1),
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.BR sync (1)
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