f3c777d5ea
Allows to use /dev/random for generating the master key instead of the default Go implementation. When the kernel random generator has been properly initialized both are considered equally secure, however: * Versions of Go prior to 1.9 just fall back to /dev/urandom if the getrandom() syscall would be blocking (Go Bug #19274) * Kernel versions prior to 3.17 do not support getrandom(), and there is no check if the random generator has been properly initialized before reading from /dev/urandom This is especially useful for embedded hardware with low-entroy. Please note that generation of the master key might block indefinitely if the kernel cannot harvest enough entropy.
339 lines
12 KiB
Markdown
339 lines
12 KiB
Markdown
% GOCRYPTFS(1)
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% github.com/rfjakob
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% Aug 2017
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NAME
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====
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gocryptfs - mount an encrypted directory
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SYNOPSIS
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========
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#### Initialize encrypted filesystem
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gocryptfs -init \[OPTIONS\] CIPHERDIR
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#### Mount
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gocryptfs \[OPTIONS\] CIPHERDIR MOUNTPOINT \[-o COMMA-SEPARATED-OPTIONS\]
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#### Change password
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gocryptfs -passwd \[OPTIONS\] CIPHERDIR
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DESCRIPTION
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===========
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Available options are listed below.
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#### -aessiv
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Use the AES-SIV encryption mode. This is slower than GCM but is
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secure with deterministic nonces as used in "-reverse" mode.
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#### -allow_other
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By default, the Linux kernel prevents any other user (even root) to
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access a mounted FUSE filesystem. Settings this option allows access for
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other users, subject to file permission checking. Only works if
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user_allow_other is set in /etc/fuse.conf. This option is equivalent to
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"allow_other" plus "default_permissions" described in fuse(8).
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#### -config string
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Use specified config file instead of CIPHERDIR/gocryptfs.conf
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#### -cpuprofile string
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Write cpu profile to specified file
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#### -ctlsock string
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Create a control socket at the specified location. The socket can be
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used to decrypt and encrypt paths inside the filesystem. When using
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this option, make sure that the direcory you place the socket in is
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not world-accessible. For example, `/run/user/UID/my.socket` would
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be suitable.
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#### -d, -debug
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Enable debug output
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#### -devrandom
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Use /dev/random for generating the master key instead of the default Go
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implementation. This is especially useful on embedded systems with Go versions
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prior to 1.9, which fall back to weak random data when the getrandom syscall
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is blocking. Using this option can block indefinitely when the kernel cannot
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harvest enough entropy.
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#### -extpass string
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Use an external program (like ssh-askpass) for the password prompt.
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The program should return the password on stdout, a trailing newline is
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stripped by gocryptfs. Using something like "cat /mypassword.txt" allows
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to mount the gocryptfs filesytem without user interaction.
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#### -fg, -f
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Stay in the foreground instead of forking away. Implies "-nosyslog".
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For compatability, "-f" is also accepted, but "-fg" is preferred.
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#### -force_owner string
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If given a string of the form "uid:gid" (where both "uid" and "gid" are
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substituted with positive integers), presents all files as owned by the given
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uid and gid, regardless of their actual ownership. Implies "allow_other".
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This is rarely desired behavior: One should *usually* run gocryptfs as the
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account which owns the backing-store files, which should *usually* be one and
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the same with the account intended to access the decrypted content. An example
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of a case where this may be useful is a situation where content is stored on a
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filesystem that doesn't properly support UNIX ownership and permissions.
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#### -forcedecode
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Force decode of encrypted files even if the integrity check fails, instead of
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failing with an IO error. Warning messages are still printed to syslog if corrupted
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files are encountered.
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It can be useful to recover files from disks with bad sectors or other corrupted
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media. It shall not be used if the origin of corruption is unknown, specially
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if you want to run executable files.
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For corrupted media, note that you probably want to use dd_rescue(1)
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instead, which will recover all but the corrupted 4kB block.
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This option makes no sense in reverse mode. It requires gocryptfs to be compiled with openssl
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support and implies -openssl true. Because of this, it is not compatible with -aessiv,
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that uses built-in Go crypto.
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Setting this option forces the filesystem to read-only and noexec.
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#### -fsname string
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Override the filesystem name (first column in df -T). Can also be
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passed as "-o fsname=" and is equivalent to libfuse's option of the
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same name. By default, CIPHERDIR is used.
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#### -fusedebug
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Enable fuse library debug output
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#### -h, -help
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Print a short help text that shows the more-often used options.
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#### -hh
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Long help text, shows all available options.
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#### -hkdf
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Use HKDF to derive separate keys for content and name encryption from
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the master key.
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#### -info
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Pretty-print the contents of the config file for human consumption,
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stripping out sensitive data.
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#### -init
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Initialize encrypted directory
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#### -ko
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Pass additonal mount options to the kernel (comma-separated list).
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FUSE filesystems are mounted with "nodev,nosuid" by default. If gocryptfs
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runs as root, you can enable device files by passing the opposite mount option,
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"dev", and if you want to enable suid-binaries, pass "suid".
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"ro" (equivalent to passing the "-ro" option) and "noexec" may also be
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interesting. For a complete list see the section
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`FILESYSTEM-INDEPENDENT MOUNT OPTIONS` in mount(8).
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#### -longnames
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Store names longer than 176 bytes in extra files (default true)
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This flag is useful when recovering old gocryptfs filesystems using
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"-masterkey". It is ignored (stays at the default) otherwise.
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#### -masterkey string
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Use a explicit master key specified on the command line. This
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option can be used to mount a gocryptfs filesystem without a config file.
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Note that the command line, and with it the master key, is visible to
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anybody on the machine who can execute "ps -auxwww".
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This is meant as a recovery option for emergencies, such as if you have
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forgotten the password or lost the config file.
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Even if a config file exists, it will not be used. All non-standard
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settings have to be passed on the command line: `-aessiv` when you
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mount a filesystem that was created using reverse mode, or
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`-plaintextnames` for a filesystem that was created with that option.
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Example master key:
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6f717d8b-6b5f8e8a-fd0aa206-778ec093-62c5669b-abd229cd-241e00cd-b4d6713d
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#### -memprofile string
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Write memory profile to the specified file. This is useful when debugging
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memory usage of gocryptfs.
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#### -nonempty
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Allow mounting over non-empty directories. FUSE by default disallows
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this to prevent accidential shadowing of files.
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#### -noprealloc
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Disable preallocation before writing. By default, gocryptfs
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preallocates the space the next write will take using fallocate(2)
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in mode FALLOC_FL_KEEP_SIZE. The preallocation makes sure it cannot
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run out of space in the middle of the write, which would cause the
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last 4kB block to be corrupt and unreadable.
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On ext4, preallocation is fast and does not cause a
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noticeable performance hit. Unfortunately, on Btrfs, preallocation
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is very slow, especially on rotational HDDs. The "-noprealloc"
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option gives users the choice to trade robustness against
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out-of-space errors for a massive speedup.
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For benchmarks and more details of the issue see
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https://github.com/rfjakob/gocryptfs/issues/63 .
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#### -nosyslog
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Diagnostic messages are normally redirected to syslog once gocryptfs
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daemonizes. This option disables the redirection and messages will
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continue be printed to stdout and stderr.
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#### -notifypid int
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Send USR1 to the specified process after successful mount. This is
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used internally for daemonization.
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#### -o COMMA-SEPARATED-OPTIONS
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For compatibility with mount(1), options are also accepted as
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"-o COMMA-SEPARATED-OPTIONS" at the end of the command line.
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For example, "-o q,zerokey" is equivalent to passing "-q -zerokey".
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#### -openssl bool/"auto"
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Use OpenSSL instead of built-in Go crypto (default "auto"). Using
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built-in crypto is 4x slower unless your CPU has AES instructions and
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you are using Go 1.6+. In mode "auto", gocrypts chooses the faster
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option.
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#### -passfile string
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Read password from the specified file. This is a shortcut for
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specifying '-extpass="/bin/cat -- FILE"'.
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#### -passwd
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Change the password. Will ask for the old password, check if it is
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correct, and ask for a new one.
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This can be used together with `-masterkey` if
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you forgot the password but know the master key. Note that without the
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old password, gocryptfs cannot tell if the master key is correct and will
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overwrite the old one without mercy. It will, however, create a backup copy
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of the old config file as `gocryptfs.conf.bak`. Delete it after
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you have verified that you can access your files with the
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new password.
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#### -plaintextnames
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Do not encrypt file names and symlink targets
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#### -q, -quiet
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Quiet - silence informational messages
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#### -raw64
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Use unpadded base64 encoding for file names. This gets rid of the
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trailing "\\=\\=". A filesystem created with this option can only be
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mounted using gocryptfs v1.2 and higher.
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#### -reverse
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Reverse mode shows a read-only encrypted view of a plaintext
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directory. Implies "-aessiv".
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#### -ro
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Mount the filesystem read-only
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#### -scryptn int
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scrypt cost parameter expressed as scryptn=log2(N). Possible values are
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10 to 28, representing N=2^10 to N=2^28.
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Setting this to a lower
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value speeds up mounting and reduces its memory needs, but makes
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the password susceptible to brute-force attacks. The default is 16.
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#### -serialize_reads
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The kernel usually submits multiple concurrent reads to service
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userspace requests and kernel readahead. gocryptfs serves them
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concurrently and in arbitrary order. On backing storage that performs
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poorly for concurrent or out-of-order reads (like Amazon Cloud Drive),
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this behavoir can cause very slow read speeds.
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The `-serialize_reads`
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option does two things: (1) reads will be submitted one-by-one (no
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concurrency) and (2) gocryptfs tries to order the reads by file
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offset order.
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The ordering requires gocryptfs to wait a certain time before
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submitting a read. The serialization introduces extra locking.
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These factors will limit throughput to below 70MB/s.
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For more details visit https://github.com/rfjakob/gocryptfs/issues/92 .
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#### -sharedstorage
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Enable work-arounds so gocryptfs works better when the backing
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storage directory is concurrently accessed by multiple gocryptfs
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instances.
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At the moment, it does two things:
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1. Disable stat() caching so changes to the backing storage show up
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immediately.
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2. Disable hard link tracking, as the inode numbers on the backing
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storage are not stable when files are deleted and re-created behind
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our back. This would otherwise produce strange "file does not exist"
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and other errors.
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When "-sharedstorage" is active, performance is reduced and hard
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links cannot be created.
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Even with this flag set, you may hit occasional problems. Running
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gocryptfs on shared storage does not receive as much testing as the
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usual (exclusive) use-case. Please test your workload in advance
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and report any problems you may hit.
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More info: https://github.com/rfjakob/gocryptfs/issues/156
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#### -speed
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Run crypto speed test. Benchmark Go's built-in GCM against OpenSSL
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(if available). The library that will be selected on "-openssl=auto"
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(the default) is marked as such.
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#### -trace string
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Write execution trace to file. View the trace using "go tool trace FILE".
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#### -version
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Print version and exit. The output contains three fields seperated by ";".
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Example: "gocryptfs v1.1.1-5-g75b776c; go-fuse 6b801d3; 2016-11-01 go1.7.3".
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Field 1 is the gocryptfs version, field 2 is the version of the go-fuse
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library, field 3 is the compile date and the Go version that was
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used.
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#### -wpanic
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When encountering a warning, panic and exit immediately. This is
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useful in regression testing.
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#### -zerokey
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Use all-zero dummy master key. This options is only intended for
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automated testing as it does not provide any security.
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#### --
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Stop option parsing. Helpful when CIPHERDIR may start with a
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dash "-".
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EXAMPLES
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========
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Create an encrypted filesystem in directory "g1" and mount it on "g2":
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mkdir g1 g2
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gocryptfs -init g1
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gocryptfs g1 g2
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Mount an ecrypted view of joe's home directory using reverse mode:
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mkdir /home/joe.crypt
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gocryptfs -init -reverse /home/joe
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gocryptfs -reverse /home/joe /home/joe.crypt
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EXIT CODES
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==========
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0: success
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6: CIPHERDIR is not an empty directory (on "-init")
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10: MOUNTPOINT is not an empty directory
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12: password incorrect
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22: password is empty (on "-init")
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23: could not read gocryptfs.conf
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24: could not write gocryptfs.conf (on "-init" or "-password")
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other: please check the error message
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SEE ALSO
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========
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fuse(8) fallocate(2)
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