Ubuntu Manpage: gocryptfs - mount an encrypted directory

Provided by: gocryptfs_1.4.3-5build1_amd64

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

Available options are listed below.

-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 directory
you place the socket in is not world-accessible. For example, /run/user/UID/my.socket
would be suitable.

-d, -debug
Enable debug output

-devrandom
Use /dev/random for generating the master key instead of the default Go implementation.
This is especially useful on embedded systems with Go versions prior to 1.9, which fall
back to weak random data when the getrandom syscall is blocking. Using this option can
block indefinitely when the kernel cannot harvest enough entropy.

-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 one to mount the gocryptfs filesystem without
user interaction.

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

-force_owner string
If given a string of the form "uid:gid" (where both "uid" and "gid" are substituted with
positive integers), presents all files as owned by the given uid and gid, regardless of
their actual ownership. Implies "allow_other".

This is rarely desired behavior: One should usually run gocryptfs as the account which
owns the backing-store files, which should usually be one and the same with the account
intended to access the decrypted content. An example of a case where this may be useful
is a situation where content is stored on a filesystem that doesn't properly support UNIX
ownership and permissions.

-forcedecode
Force decode of encrypted files even if the integrity check fails, instead of failing with
an IO error. Warning messages are still printed to syslog if corrupted files are
encountered. It can be useful to recover files from disks with bad sectors or other
corrupted media. It shall not be used if the origin of corruption is unknown, specially
if you want to run executable files.

For corrupted media, note that you probably want to use dd_rescue(1) instead, which will
recover all but the corrupted 4kB block.

This option makes no sense in reverse mode. It requires gocryptfs to be compiled with
openssl support and implies -openssl true. Because of this, it is not compatible with
-aessiv, that uses built-in Go crypto.

Setting this option forces the filesystem to read-only and noexec.

-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

-h, -help
Print a short help text that shows the more-often used options.

-hh
Long help text, shows all available options.

-hkdf
Use HKDF to derive separate keys for content and name encryption from the master key.

-info
Pretty-print the contents of the config file for human consumption, stripping out
sensitive data.

-init
Initialize encrypted directory

-ko
Pass additional 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). On MacOS, "local", "noapplexattr",
"noappledouble" may be interesting.

Note that unlike "-o", "-ko" is a regular option and must be passed BEFORE the
directories. Example:

gocryptfs -ko noexec /tmp/foo /tmp/bar

-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 the password or
lost the config file.

Even if a config file exists, it will not be used. All non-standard settings have to be
passed on the command line: -aessiv when you mount a filesystem that was created using
reverse mode, or -plaintextnames for a filesystem that was created with that option.

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
accidental 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".

Note that you can only use options that are understood by gocryptfs with "-o". If you
want to pass special flags to the kernel, you should use "-ko" (kernel option). This is
different in libfuse-based filesystems, that automatically pass any "-o" options they do
not understand along to the kernel.

Example:

gocryptfs /tmp/foo /tmp/bar -o 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 behavior 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 .

-sharedstorage
Enable work-arounds so gocryptfs works better when the backing storage directory is
concurrently accessed by multiple gocryptfs instances.

At the moment, it does two things:

1. Disable stat() caching so changes to the backing storage show up immediately.

2. Disable hard link tracking, as the inode numbers on the backing storage are not stable
when files are deleted and re-created behind our back. This would otherwise produce
strange "file does not exist" and other errors.

When "-sharedstorage" is active, performance is reduced and hard links cannot be created.

Even with this flag set, you may hit occasional problems. Running gocryptfs on shared
storage does not receive as much testing as the usual (exclusive) use-case. Please test
your workload in advance and report any problems you may hit.

More info: https://github.com/rfjakob/gocryptfs/issues/156

-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.

-trace string
Write execution trace to file. View the trace using "go tool trace FILE".

-version
Print version and exit. The output contains three fields separated 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
       6: CIPHERDIR is not an empty directory (on "-init")
       10: MOUNTPOINT is not an empty directory
       12: password incorrect
       22: password is empty (on "-init")
       23: could not read gocryptfs.conf
       24: could not write gocryptfs.conf (on "-init" or "-password")
       other: please check the error message

AUTHORS