GOCRYPTFS(1) GOCRYPTFS(1)

gocryptfs - create or mount an encrypted filesystem

gocryptfs -init [OPTIONS] CIPHERDIR

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

fusermount -u MOUNTPOINT

gocryptfs -passwd [OPTIONS] CIPHERDIR

gocryptfs -fsck [OPTIONS] CIPHERDIR

gocryptfs -info [OPTIONS] CIPHERDIR

gocryptfs is an encrypted overlay filesystem written in Go. Encrypted files are stored in CIPHERDIR, and a plain-text view can be presented by mounting the filesystem at MOUNTPOINT.

gocryptfs was inspired by encfs(1) and strives to fix its security issues while providing good performance.

Unless one of the following action flags is passed, the default action is to mount a filesystem (see SYNOPSIS).

Check CIPHERDIR for consistency. If corruption is found, the exit code is 26.

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

Long help text, shows all available options.

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

Example:

$ gocryptfs -info my_cipherdir
Creator:      gocryptfs v2.0-beta2
FeatureFlags: GCMIV128 HKDF DirIV EMENames LongNames Raw64
EncryptedKey: 64B
ScryptObject: Salt=32B N=65536 R=8 P=1 KeyLen=32

Initialize encrypted directory.

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.

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.

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.

Available options for -init are listed below. Usually, you don’t need any. Defaults are fine.

Use the AES-SIV encryption mode. This is slower than AES-GCM but is secure with deterministic nonces as used in “-reverse” mode.

Run gocryptfs -speed to find out if and how much slower.

Disable file name randomisation and creation of gocryptfs.diriv files. This can prevent sync conflicts conflicts when synchronising files, but leaks information about identical file names across directories (“Identical names leak” in https://nuetzlich.net/gocryptfs/comparison/#file-names ).

The resulting gocryptfs.conf has “DirIV” missing from “FeatureFlags”.

Obsolete and ignored on gocryptfs v2.2 and later.

See https://github.com/rfjakob/gocryptfs/commit/f3c777d5eaa682d878c638192311e52f9c204294 and https://github.com/rfjakob/gocryptfs/issues/596 for background info.

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

integer value, allowed range 62...255

Hash file names that (in encrypted form) exceed this length. The default is 255, which aligns with the usual name length limit on Linux and provides best performance.

However, online storage may impose lower limits on file name and/or path length. In this case, setting -longnamemax to a lower value can be helpful.

The lower the value, the more extra .name files must be created, which slows down directory listings.

Values below 62 are not allowed as then the hashed name would be longer than the original name.

Example:

-longnamemax 100

Do not encrypt file names and symlink targets.

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. Default true.

Reverse mode shows a read-only encrypted view of a plaintext directory. Implies “-aessiv”.

Use XChaCha20-Poly1305 file content encryption. This should be much faster than AES-GCM on CPUs that lack AES acceleration.

Run gocryptfs -speed to find out if and how much faster.

Available options for mounting are listed below. Usually, you don’t need any. Defaults are fine.

Enable ACL enforcement. When you want to use ACLs, you must enable this option.

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).

When gocryptfs encounters a “bad” file name (cannot be decrypted or decrypts to garbage), a warning is logged and the file is hidden from the plaintext view.

With the -badname option, you can select “bad” file names that should still be shown in the plaintext view instead of hiding them. Bad files will get GOCRYPTFS_BAD_NAME appended to their name.

Glob pattern. Can be passed multiple times for multiple patterns.

Examples:

Dropbox sync conflicts:

-badname '*conflicted copy*'

Syncthing sync conflicts:

-badname '*.sync-conflict*'

Show all invalid filenames:

-badname '*'

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.

Enable (-dev) or disable (-nodev) device files in a gocryptfs mount (default: -nodev). If both are specified, -nodev takes precedence. You need root permissions to use -dev.

Only for reverse mode: exclude relative plaintext path from the encrypted view, matching only from root of mounted filesystem. Can be passed multiple times.

Example that excludes the directories “Music” and “Movies” from the root directory:

gocryptfs -reverse -exclude Music -exclude Movies /home/user /mnt/user.encrypted

See also -exclude-wildcard, -exclude-from and the EXCLUDING FILES section.

Only for reverse mode: exclude paths from the encrypted view in gitignore(5) syntax, wildcards supported. Pass multiple times for multiple patterns.

Example to exclude all .mp3 files in any directory:

gocryptfs -reverse -exclude-wildcard '*.mp3' /home/user /mnt/user.encrypted

Example to to exclude everything but the directory `important' in the root dir:

gocryptfs -reverse -exclude-wildcard '*' -exclude-wildcard '!/important' /home/user /mnt/user.encrypted

See also -exclude-from and the EXCLUDING FILES section.

Only for reverse mode: reads gitignore patterns from a file. Can be passed multiple times. Example:

gocryptfs -reverse -exclude-from ~/crypt-exclusions /home/user /mnt/user.encrypted

See also -exclude, -exclude-wildcard and the EXCLUDING FILES section.

Enable (-exec) or disable (-noexec) executables in a gocryptfs mount (default: -exec). If both are specified, -noexec takes precedence.

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

Unless -notifypid is also passed, the logs go to stdout and stderr instead of syslog.

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.

Obsolete and ignored on gocryptfs v2.2 and later.

See https://github.com/rfjakob/gocryptfs/commit/d023cd6c95fcbc6b5056ba1f425d2ac3df4abc5a for what it was and why it was dropped.

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.

Enable fuse library debug output.

Only for forward mode: automatically unmount the filesystem if it has been idle for the specified duration. Durations can be specified like “500s” or “2h45m”. 0 (the default) means stay mounted indefinitely.

When a process has open files or its working directory in the mount, this will keep it not idle indefinitely.

Enable the kernel_cache option of the FUSE filesystem, see fuse(8) for details.

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” enables volume-based trash if you have .Trashes folder in the root of your volume (might need to be manually created) note, though, that “local” is marked as “experimental” in osxfuse (https://github.com/osxfuse/osxfuse/wiki/Mount-options#local); “noapplexattr”, “noappledouble” may also 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

Store names that are longer than 175 bytes in extra files (default true).

This flag is only useful when recovering very old gocryptfs filesystems (gocryptfs v0.8 and earlier) using “-masterkey”. It is ignored (stays at the default) otherwise.

See -dev, -nodev.

See -exec, -noexec.

Having the nofail option in /etc/fstab instructs systemd to continue booting normally even if the mount fails (see man systemd.fstab).

The option is ignored by gocryptfs itself and has no effect outside /etc/fstab.

Allow mounting over non-empty directories. FUSE by default disallows this to prevent accidental shadowing of files.

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 .

See -suid, -nosuid.

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.

Send USR1 to the specified process after successful mount. This is used internally for daemonization.

Don’t cross filesystem boundaries (like rsync’s --one-file-system). Mountpoints will appear as empty directories.

Only applicable to reverse mode.

Limitation: Mounted single files (yes this is possible) are NOT hidden.

Mount the filesystem read-write (-rw, default) or read-only (-ro). If both are specified, -ro takes precedence.

See the -reverse section in INIT FLAGS. You need to specify the -reverse option both at -init and at mount.

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 .

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

Enable (-suid) or disable (-nosuid) suid and sgid executables in a gocryptfs mount (default: -nosuid). If both are specified, -nosuid takes precedence. You need root permissions to use -suid.

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

Options that apply to more than one action are listed below. Each options lists where it is applicable. Again, usually you don’t need any.

Use specified config file instead of CIPHERDIR/gocryptfs.conf.

Applies to: all actions that use a config file: mount, -fsck, -passwd, -info, -init.

Write cpu profile to specified file.

Applies to: all actions.

Enable debug output.

Applies to: all actions.

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. If you just want to read from a password file, see -passfile.

When -extpass is specified once, the string argument will be split on spaces. For example, -extpass "md5sum my password.txt" will be executed as "md5sum" "my" "password.txt", which is NOT what you want.

Specify -extpass twice or more to use the string arguments as-is. For example, you DO want to call md5sum like this: -extpass "md5sum" -extpass "my password.txt".

If you want to prevent splitting on spaces but don’t want to pass arguments to your program, use "--", which is accepted by most programs: -extpass "my program" -extpass "--"

Applies to: all actions that ask for a password.

BUG: In -extpass -X, the -X will be interpreted as --X. Please use -extpass=-X to prevent that. See Dash duplication in the BUGS section for details.

Use a FIDO2 token to initialize and unlock the filesystem. Use “fido2-token -L” to obtain the FIDO2 token device path. For linux, “fido2-tools” package is needed.

Applies to: all actions that ask for a password.

Use an explicit master key specified on the command line or, if the special value “stdin” is used, read the masterkey from stdin, instead of reading the config file and asking for the decryption password.

Note that the command line, and with it the master key, is visible to anybody on the machine who can execute “ps -auxwww”. Use “-masterkey=stdin” to avoid that risk.

The masterkey option 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.

Examples:

-masterkey=6f717d8b-6b5f8e8a-fd0aa206-778ec093-62c5669b-abd229cd-241e00cd-b4d6713d
-masterkey=stdin

Applies to: all actions that ask for a password.

Write memory profile to the specified file. This is useful when debugging memory usage of gocryptfs.

Applies to: all actions.

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

Applies to: all actions.

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.

Applies to: all actions.

Read password from the specified plain text file. The file should contain exactly one line (do not use binary files!). A warning will be printed if there is more than one line, and only the first line will be used. A single trailing newline is allowed and does not cause a warning.

Pass this option multiple times to read the first line from multiple files. They are concatenated for the effective password.

Example:

echo hello > hello.txt
echo word > world.txt
gocryptfs -passfile hello.txt -passfile world.txt

The effective password will be “helloworld”.

Applies to: all actions that ask for a password.

Quiet - silence informational messages.

Applies to: all actions.

gocryptfs uses scrypt for hashing the password when mounting, which protects from brute-force attacks.

-scryptn controls the scrypt cost parameter “N” expressed as scryptn=log2(N). Possible values are -scryptn=10 to -scryptn=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.

The memory usage for scrypt during mounting is as follows:

scryptn     Memory Usage  
=======     ============
10          1   MiB
11          2 
12          4 
13          8 
14          16  
15          32  
16          64  
17          128 
18          256 
19          512 
20          1   GiB
21          2 
22          4 
23          8 
24          16  
25          32  
26          64  
27          128 
28          256

Applies to: -init, -passwd

See also: the benchmarks in the gocryptfs source code in internal/configfile.

Write execution trace to file. View the trace using “go tool trace FILE”.

Applies to: all actions.

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

Applies to: all actions.

Stop option parsing. Helpful when CIPHERDIR may start with a dash “-”.

Applies to: all actions.

In reverse mode, it is possible to exclude files from the encrypted view, using the -exclude, -exclude-wildcard and -exclude-from options.

-exclude matches complete paths, so -exclude file.txt only excludes a file named file.txt in the root of the mounted filesystem; files named file.txt in subdirectories are still visible. Wildcards are NOT supported. This option is kept for compatibility with the behavior up to version 1.6.x. New users should use -exclude-wildcard instead.

-exclude-wildcard uses gitignore syntax and matches files anywhere, so -exclude-wildcard file.txt excludes files named file.txt in any directory. If you want to match complete paths, you can prefix the filename with a /: -exclude-wildcard /file.txt excludes only file.txt in the root of the mounted filesystem.

If there are many exclusions, you can use -exclude-from to read gitignore patterns from a file. As with -exclude-wildcard, use a leading / to match complete paths.

The rules for exclusion are that of gitignore (https://git-scm.com/docs/gitignore#_pattern_format). In short:

1.
A blank line matches no files, so it can serve as a separator for readability.
2.
A line starting with # serves as a comment. Put a backslash (\) in front of the first hash for patterns that begin with a hash.
3.
Trailing spaces are ignored unless they are quoted with backslash (\).
4.
An optional prefix ! negates the pattern; any matching file excluded by a previous pattern will become included again. It is not possible to re-include a file if a parent directory of that file is excluded. Put a backslash (\) in front of the first ! for patterns that begin with a literal !, for example, \!important!.txt.
5.
If the pattern ends with a slash, it is removed for the purpose of the following description, but it would only find a match with a directory. In other words, foo/ will match a directory foo and paths underneath it, but will not match a regular file or a symbolic link foo.
6.
If the pattern does not contain a slash /, it is treated as a shell glob pattern and checked for a match against the pathname relative to the root of the mounted filesystem.
7.
Otherwise, the pattern is treated as a shell glob suitable for consumption by fnmatch(3) with the FNM_PATHNAME flag: wildcards in the pattern will not match a / in the pathname. For example, Documentation/*.html matches Documentation/git.html but not Documentation/ppc/ppc.html or tools/perf/Documentation/perf.html.
8.
A leading slash matches the beginning of the pathname. For example, /*.c matches cat-file.c but not mozilla-sha1/sha1.c.
9.
Two consecutive asterisks (**) in patterns matched against full pathname may have special meaning:
A leading ** followed by a slash means match in all directories. For example, **/foo matches file or directory foo anywhere, the same as pattern foo. **/foo/bar matches file or directory bar anywhere that is directly under directory foo.
A trailing /** matches everything inside. For example, abc/** matches all files inside directory abc, with infinite depth.
A slash followed by two consecutive asterisks then a slash matches zero or more directories. For example, a/**/b matches a/b, a/x/b, a/x/y/b and so on.
Other consecutive asterisks are considered invalid.

Create an encrypted filesystem in directory “mydir.crypt”, mount it on “mydir”:

mkdir mydir.crypt mydir
gocryptfs -init mydir.crypt
gocryptfs mydir.crypt mydir

Mount an encrypted 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

Adding this line to /etc/fstab will mount /tmp/cipher to /tmp/plain on boot, using the password in /tmp/passfile. Use sudo mount -av to test the line without having to reboot. Adjust the gocryptfs path acc. to the output of the command which gocryptfs. Do use the nofail option to prevent an unbootable system if the gocryptfs mount fails (see the -nofail option for details).

/tmp/cipher /tmp/plain fuse./usr/local/bin/gocryptfs nofail,allow_other,passfile=/tmp/password 0 0

If NO_COLOR is set (regardless of value), colored output is disabled (see https://no-color.org/).

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”)

26: fsck found errors

other: please check the error message

See also: https://github.com/rfjakob/gocryptfs/blob/master/internal/exitcodes/exitcodes.go

gocryptfs v2.1 switched to the pflag library for command-line parsing to support flags and positional arguments in any order. To stay compatible with single-dash long options like -extpass, an ugly hack was added: The command line is preprocessed, and all single-dash options are converted to double-dash.

Unfortunately, this means that in

gocryptfs -extpass myapp -extpass -X

gocryptfs transforms the -X to --X, and it will call myapp --X as the extpass program.

Please use

gocryptfs -extpass myapp -extpass=-X

to work around this bug.

mount(2) fuse(8) fallocate(2) encfs(1) gitignore(5)

github.com/rfjakob.

Aug 2017