path: root/Documentation/MANPAGE.md

% GOCRYPTFS(1)
% github.com/rfjakob
% Oct 2016

NAME
====

gocryptfs - mount an encrypted directory

SYNOPSIS
========

Initialize encrypted filesystem
-------------------------------

gocryptfs -init [OPTIONS] CIPHERDIR

Mount
-----

gocryptfs [OPTIONS] CIPHERDIR MOUNTPOINT [-o COMMA-SEPARATED-OPTIONS]

Change password
---------------

gocryptfs -passwd [OPTIONS] CIPHERDIR

DESCRIPTION
===========

Options:

**-aessiv**
:	Use the AES-SIV encryption mode. This is slower than GCM but is
	secure with deterministic nonces as used in "-reverse" mode.

**-allow_other**
:	By default, the Linux kernel prevents any other user (even root) to
	access a mounted FUSE filesystem. Settings this option allows access for
	other users, subject to file permission checking. Only works if
	user_allow_other is set in /etc/fuse.conf. This option is equivalent to
	"allow_other" plus "default_permissions" described in fuse(8).

**-config string**
:	Use specified config file instead of CIPHERDIR/gocryptfs.conf

**-cpuprofile string**
:	Write cpu profile to specified file

**-ctlsock string**
:	Create a control socket at the specified location. The socket can be
	used to decrypt and encrypt paths inside the filesystem. When using
	this option, make sure that the direcory you place the socket in is
	not world-accessible. For example, `/run/user/UID/my.socket` would 
	be suitable.

**-d, -debug**
:	Enable debug output

**-extpass string**
:	Use an external program (like ssh-askpass) for the password prompt.
	The program should return the password on stdout, a trailing newline is
	stripped by gocryptfs. Using something like "cat /mypassword.txt" allows
	to mount the gocryptfs filesytem without user interaction.

**-fg, -f**
:	Stay in the foreground instead of forking away. Implies "-nosyslog".
	For compatability, "-f" is also accepted, but "-fg" is preferred.

**-fsname string**
:	Override the filesystem name (first column in df -T). Can also be
	passed as "-o fsname=" and is equivalent to libfuse's option of the
	same name. By default, CIPHERDIR is used.

**-fusedebug**
:	Enable fuse library debug output

**-init**
:	Initialize encrypted directory

**-ko**
:	Pass additonal mount options to the kernel (comma-separated list).
	FUSE filesystems are mounted with "nodev,nosuid" by default. If gocryptfs
	runs as root, you can enable device files by passing the opposite mount option,
	"dev", and if you want to enable suid-binaries, pass "suid".
	"ro" (equivalent to passing the "-ro" option) and "noexec" may also be
	interesting. For a complete list see the section
	`FILESYSTEM-INDEPENDENT MOUNT OPTIONS` in mount(8).

**-longnames**
:	Store names longer than 176 bytes in extra files (default true)
	This flag is useful when recovering old gocryptfs filesystems using
	"-masterkey". It is ignored (stays at the default) otherwise.

**-masterkey string**
:	Use a explicit master key specified on the command line. This
	option can be used to mount a gocryptfs filesystem without a config file.
	Note that the command line, and with it the master key, is visible to
	anybody on the machine who can execute "ps -auxwww".
	This is meant as a recovery option for emergencies, such as if you have
	forgotten your password.
	
	Example master key:  
	6f717d8b-6b5f8e8a-fd0aa206-778ec093-62c5669b-abd229cd-241e00cd-b4d6713d

**-memprofile string**
:	Write memory profile to the specified file. This is useful when debugging
	memory usage of gocryptfs.

**-nonempty**
:	Allow mounting over non-empty directories. FUSE by default disallows
	this to prevent accidential shadowing of files.

**-noprealloc**
:	Disable preallocation before writing. By default, gocryptfs
	preallocates the space the next write will take using fallocate(2)
	in mode FALLOC_FL_KEEP_SIZE. The preallocation makes sure it cannot
	run out of space in the middle of the write, which would cause the
	last 4kB block to be corrupt and unreadable.

	On ext4, preallocation is fast and does not cause a
	noticeable performance hit. Unfortunately, on Btrfs, preallocation
	is very slow, especially on rotational HDDs. The "-noprealloc"
	option gives users the choice to trade robustness against
	out-of-space errors for a massive speedup.
	
	For benchmarks and more details of the issue see
	https://github.com/rfjakob/gocryptfs/issues/63 .

**-nosyslog**
:	Diagnostic messages are normally redirected to syslog once gocryptfs
	daemonizes. This option disables the redirection and messages will
	continue be printed to stdout and stderr.

**-notifypid int**
:	Send USR1 to the specified process after successful mount. This is
	used internally for daemonization.

**-o COMMA-SEPARATED-OPTIONS**
:	For compatibility with mount(1), options are also accepted as
	"-o COMMA-SEPARATED-OPTIONS" at the end of the command line.
	For example, "-o q,zerokey" is equivalent to passing "-q -zerokey".

**-openssl bool/"auto"**
:	Use OpenSSL instead of built-in Go crypto (default "auto"). Using
	built-in crypto is 4x slower unless your CPU has AES instructions and
	you are using Go 1.6+. In mode "auto", gocrypts chooses the faster
	option.

**-passfile string**
:	Read password from the specified file. This is a shortcut for
	specifying '-extpass="/bin/cat -- FILE"'.

**-passwd**
:	Change the password. Will ask for the old password, check if it is
	correct, and ask for a new one.
	
	This can be used together with `-masterkey` if
	you forgot the password but know the master key. Note that without the
	old password, gocryptfs cannot tell if the master key is correct and will
	overwrite the old one without mercy. It will, however, create a backup copy
	of the old config file as `gocryptfs.conf.bak`. Delete it after
	you have verified that you can access your files with the
	new password.

**-plaintextnames**
:	Do not encrypt file names and symlink targets

**-q, -quiet**
:	Quiet - silence informational messages

**-raw64**
:	Use unpadded base64 encoding for file names. This gets rid of the
	trailing "\\=\\=". A filesystem created with this option can only be
	mounted using gocryptfs v1.2 and higher.

**-reverse**
:	Reverse mode shows a read-only encrypted view of a plaintext
	directory. Implies "-aessiv".

**-ro**
:	Mount the filesystem read-only

**-scryptn int**
:	scrypt cost parameter expressed as scryptn=log2(N). Possible values are
	10 to 28, representing N=2^10 to N=2^28.
	
	Setting this to a lower
	value speeds up mounting and reduces its memory needs, but makes
	the password susceptible to brute-force attacks. The default is 16.

**-serialize_reads**
:	The kernel usually submits multiple concurrent reads to service
	userspace requests and kernel readahead. gocryptfs serves them
	concurrently and in arbitrary order. On backing storage that performs
	poorly for concurrent or out-of-order reads (like Amazon Cloud Drive),
	this behavoir can cause very slow read speeds.
	
	The `-serialize_reads`
	option does two things: (1) reads will be submitted one-by-one (no
	concurrency) and (2) gocryptfs tries to order the reads by file
	offset order.
	
	The ordering requires gocryptfs to wait a certain time before
	submitting a read. The serialization introduces extra locking.
	These factors will limit throughput to below 70MB/s.
	
	For more details visit https://github.com/rfjakob/gocryptfs/issues/92 .

**-speed**
:	Run crypto speed test. Benchmark Go's built-in GCM against OpenSSL
	(if available). The library that will be selected on "-openssl=auto"
	(the default) is marked as such.

**-version**
:	Print version and exit. The output contains three fields seperated by ";".
	Example: "gocryptfs v1.1.1-5-g75b776c; go-fuse 6b801d3; 2016-11-01 go1.7.3".
	Field 1 is the gocryptfs version, field 2 is the version of the go-fuse
	library, field 3 is the compile date and the Go version that was
	used.

**-wpanic**
:	When encountering a warning, panic and exit immediately. This is
	useful in regression testing.

**-zerokey**
:	Use all-zero dummy master key. This options is only intended for
	automated testing as it does not provide any security.

**--**
:	Stop option parsing. Helpful when CIPHERDIR may start with a
	dash "-".

EXAMPLES
========

Create an encrypted filesystem in directory "g1" and mount it on "g2":

	mkdir g1 g2
	gocryptfs -init g1
	gocryptfs g1 g2

Mount an ecrypted view of joe's home directory using reverse mode:

	mkdir /home/joe.crypt
	gocryptfs -init -reverse /home/joe
	gocryptfs -reverse /home/joe /home/joe.crypt

EXIT CODES
==========

0: success  
12: password incorrect  
other: please check the error message

SEE ALSO
========
fuse(8) fallocate(2)