1 SSHD_CONFIG(5) File Formats Manual SSHD_CONFIG(5)
4 sshd_config M-bM-^@M-^S OpenSSH SSH daemon configuration file
10 sshd(8) reads configuration data from /etc/ssh/sshd_config (or the file
11 specified with -f on the command line). The file contains keyword-
12 argument pairs, one per line. Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines
13 are interpreted as comments. Arguments may optionally be enclosed in
14 double quotes (") in order to represent arguments containing spaces.
16 The possible keywords and their meanings are as follows (note that
17 keywords are case-insensitive and arguments are case-sensitive):
20 Specifies what environment variables sent by the client will be
21 copied into the session's environ(7). See SendEnv in
22 ssh_config(5) for how to configure the client. Note that
23 environment passing is only supported for protocol 2. Variables
24 are specified by name, which may contain the wildcard characters
25 M-bM-^@M-^X*M-bM-^@M-^Y and M-bM-^@M-^X?M-bM-^@M-^Y. Multiple environment variables may be separated by
26 whitespace or spread across multiple AcceptEnv directives. Be
27 warned that some environment variables could be used to bypass
28 restricted user environments. For this reason, care should be
29 taken in the use of this directive. The default is not to accept
30 any environment variables.
33 Specifies which address family should be used by sshd(8). Valid
34 arguments are M-bM-^@M-^\anyM-bM-^@M-^], M-bM-^@M-^\inetM-bM-^@M-^] (use IPv4 only), or M-bM-^@M-^\inet6M-bM-^@M-^] (use IPv6
35 only). The default is M-bM-^@M-^\anyM-bM-^@M-^].
38 Specifies whether ssh-agent(1) forwarding is permitted. The
39 default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that disabling agent forwarding does not
40 improve security unless users are also denied shell access, as
41 they can always install their own forwarders.
44 This keyword can be followed by a list of group name patterns,
45 separated by spaces. If specified, login is allowed only for
46 users whose primary group or supplementary group list matches one
47 of the patterns. Only group names are valid; a numerical group
48 ID is not recognized. By default, login is allowed for all
49 groups. The allow/deny directives are processed in the following
50 order: DenyUsers, AllowUsers, DenyGroups, and finally
53 See PATTERNS in ssh_config(5) for more information on patterns.
56 Specifies whether TCP forwarding is permitted. The available
57 options are M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\allM-bM-^@M-^] to allow TCP forwarding, M-bM-^@M-^\noM-bM-^@M-^] to
58 prevent all TCP forwarding, M-bM-^@M-^\localM-bM-^@M-^] to allow local (from the
59 perspective of ssh(1)) forwarding only or M-bM-^@M-^\remoteM-bM-^@M-^] to allow
60 remote forwarding only. The default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that
61 disabling TCP forwarding does not improve security unless users
62 are also denied shell access, as they can always install their
65 AllowStreamLocalForwarding
66 Specifies whether StreamLocal (Unix-domain socket) forwarding is
67 permitted. The available options are M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\allM-bM-^@M-^] to allow
68 StreamLocal forwarding, M-bM-^@M-^\noM-bM-^@M-^] to prevent all StreamLocal
69 forwarding, M-bM-^@M-^\localM-bM-^@M-^] to allow local (from the perspective of
70 ssh(1)) forwarding only or M-bM-^@M-^\remoteM-bM-^@M-^] to allow remote forwarding
71 only. The default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that disabling StreamLocal
72 forwarding does not improve security unless users are also denied
73 shell access, as they can always install their own forwarders.
76 This keyword can be followed by a list of user name patterns,
77 separated by spaces. If specified, login is allowed only for
78 user names that match one of the patterns. Only user names are
79 valid; a numerical user ID is not recognized. By default, login
80 is allowed for all users. If the pattern takes the form
81 USER@HOST then USER and HOST are separately checked, restricting
82 logins to particular users from particular hosts. The allow/deny
83 directives are processed in the following order: DenyUsers,
84 AllowUsers, DenyGroups, and finally AllowGroups.
86 See PATTERNS in ssh_config(5) for more information on patterns.
89 Specifies the authentication methods that must be successfully
90 completed for a user to be granted access. This option must be
91 followed by one or more comma-separated lists of authentication
92 method names. Successful authentication requires completion of
93 every method in at least one of these lists.
95 For example, an argument of M-bM-^@M-^\publickey,password
96 publickey,keyboard-interactiveM-bM-^@M-^] would require the user to
97 complete public key authentication, followed by either password
98 or keyboard interactive authentication. Only methods that are
99 next in one or more lists are offered at each stage, so for this
100 example, it would not be possible to attempt password or
101 keyboard-interactive authentication before public key.
103 For keyboard interactive authentication it is also possible to
104 restrict authentication to a specific device by appending a colon
105 followed by the device identifier M-bM-^@M-^\bsdauthM-bM-^@M-^], M-bM-^@M-^\pamM-bM-^@M-^], or M-bM-^@M-^\skeyM-bM-^@M-^],
106 depending on the server configuration. For example,
107 M-bM-^@M-^\keyboard-interactive:bsdauthM-bM-^@M-^] would restrict keyboard
108 interactive authentication to the M-bM-^@M-^\bsdauthM-bM-^@M-^] device.
110 If the M-bM-^@M-^\publickeyM-bM-^@M-^] method is listed more than once, sshd(8)
111 verifies that keys that have been used successfully are not
112 reused for subsequent authentications. For example, an
113 AuthenticationMethods of M-bM-^@M-^\publickey,publickeyM-bM-^@M-^] will require
114 successful authentication using two different public keys.
116 This option is only available for SSH protocol 2 and will yield a
117 fatal error if enabled if protocol 1 is also enabled. Note that
118 each authentication method listed should also be explicitly
119 enabled in the configuration. The default is not to require
120 multiple authentication; successful completion of a single
121 authentication method is sufficient.
123 AuthorizedKeysCommand
124 Specifies a program to be used to look up the user's public keys.
125 The program must be owned by root and not writable by group or
126 others. It will be invoked with a single argument of the
127 username being authenticated, and should produce on standard
128 output zero or more lines of authorized_keys output (see
129 AUTHORIZED_KEYS in sshd(8)). If a key supplied by
130 AuthorizedKeysCommand does not successfully authenticate and
131 authorize the user then public key authentication continues using
132 the usual AuthorizedKeysFile files. By default, no
133 AuthorizedKeysCommand is run.
135 AuthorizedKeysCommandUser
136 Specifies the user under whose account the AuthorizedKeysCommand
137 is run. It is recommended to use a dedicated user that has no
138 other role on the host than running authorized keys commands. If
139 AuthorizedKeysCommand is specified but AuthorizedKeysCommandUser
140 is not, then sshd(8) will refuse to start.
143 Specifies the file that contains the public keys that can be used
144 for user authentication. The format is described in the
145 AUTHORIZED_KEYS FILE FORMAT section of sshd(8).
146 AuthorizedKeysFile may contain tokens of the form %T which are
147 substituted during connection setup. The following tokens are
148 defined: %% is replaced by a literal '%', %h is replaced by the
149 home directory of the user being authenticated, and %u is
150 replaced by the username of that user. After expansion,
151 AuthorizedKeysFile is taken to be an absolute path or one
152 relative to the user's home directory. Multiple files may be
153 listed, separated by whitespace. The default is
154 M-bM-^@M-^\.ssh/authorized_keys .ssh/authorized_keys2M-bM-^@M-^].
156 AuthorizedPrincipalsFile
157 Specifies a file that lists principal names that are accepted for
158 certificate authentication. When using certificates signed by a
159 key listed in TrustedUserCAKeys, this file lists names, one of
160 which must appear in the certificate for it to be accepted for
161 authentication. Names are listed one per line preceded by key
162 options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)).
163 Empty lines and comments starting with M-bM-^@M-^X#M-bM-^@M-^Y are ignored.
165 AuthorizedPrincipalsFile may contain tokens of the form %T which
166 are substituted during connection setup. The following tokens
167 are defined: %% is replaced by a literal '%', %h is replaced by
168 the home directory of the user being authenticated, and %u is
169 replaced by the username of that user. After expansion,
170 AuthorizedPrincipalsFile is taken to be an absolute path or one
171 relative to the user's home directory.
173 The default is M-bM-^@M-^\noneM-bM-^@M-^], i.e. not to use a principals file M-bM-^@M-^S in
174 this case, the username of the user must appear in a
175 certificate's principals list for it to be accepted. Note that
176 AuthorizedPrincipalsFile is only used when authentication
177 proceeds using a CA listed in TrustedUserCAKeys and is not
178 consulted for certification authorities trusted via
179 ~/.ssh/authorized_keys, though the principals= key option offers
180 a similar facility (see sshd(8) for details).
182 Banner The contents of the specified file are sent to the remote user
183 before authentication is allowed. If the argument is M-bM-^@M-^\noneM-bM-^@M-^] then
184 no banner is displayed. This option is only available for
185 protocol version 2. By default, no banner is displayed.
187 ChallengeResponseAuthentication
188 Specifies whether challenge-response authentication is allowed
189 (e.g. via PAM or through authentication styles supported in
190 login.conf(5)) The default is M-bM-^@M-^\yesM-bM-^@M-^].
193 Specifies the pathname of a directory to chroot(2) to after
194 authentication. At session startup sshd(8) checks that all
195 components of the pathname are root-owned directories which are
196 not writable by any other user or group. After the chroot,
197 sshd(8) changes the working directory to the user's home
200 The pathname may contain the following tokens that are expanded
201 at runtime once the connecting user has been authenticated: %% is
202 replaced by a literal '%', %h is replaced by the home directory
203 of the user being authenticated, and %u is replaced by the
204 username of that user.
206 The ChrootDirectory must contain the necessary files and
207 directories to support the user's session. For an interactive
208 session this requires at least a shell, typically sh(1), and
209 basic /dev nodes such as null(4), zero(4), stdin(4), stdout(4),
210 stderr(4), and tty(4) devices. For file transfer sessions using
211 M-bM-^@M-^\sftpM-bM-^@M-^], no additional configuration of the environment is
212 necessary if the in-process sftp server is used, though sessions
213 which use logging may require /dev/log inside the chroot
214 directory on some operating systems (see sftp-server(8) for
217 For safety, it is very important that the directory hierarchy be
218 prevented from modification by other processes on the system
219 (especially those outside the jail). Misconfiguration can lead
220 to unsafe environments which sshd(8) cannot detect.
222 The default is not to chroot(2).
225 Specifies the ciphers allowed for protocol version 2. Multiple
226 ciphers must be comma-separated. The supported ciphers are:
235 aes128-gcm@openssh.com
236 aes256-gcm@openssh.com
242 chacha20-poly1305@openssh.com
246 aes128-ctr,aes192-ctr,aes256-ctr,
247 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
248 chacha20-poly1305@openssh.com
250 The list of available ciphers may also be obtained using the -Q
251 option of ssh(1) with an argument of M-bM-^@M-^\cipherM-bM-^@M-^].
254 Sets the number of client alive messages (see below) which may be
255 sent without sshd(8) receiving any messages back from the client.
256 If this threshold is reached while client alive messages are
257 being sent, sshd will disconnect the client, terminating the
258 session. It is important to note that the use of client alive
259 messages is very different from TCPKeepAlive (below). The client
260 alive messages are sent through the encrypted channel and
261 therefore will not be spoofable. The TCP keepalive option
262 enabled by TCPKeepAlive is spoofable. The client alive mechanism
263 is valuable when the client or server depend on knowing when a
264 connection has become inactive.
266 The default value is 3. If ClientAliveInterval (see below) is
267 set to 15, and ClientAliveCountMax is left at the default,
268 unresponsive SSH clients will be disconnected after approximately
269 45 seconds. This option applies to protocol version 2 only.
272 Sets a timeout interval in seconds after which if no data has
273 been received from the client, sshd(8) will send a message
274 through the encrypted channel to request a response from the
275 client. The default is 0, indicating that these messages will
276 not be sent to the client. This option applies to protocol
280 Specifies whether compression is allowed, or delayed until the
281 user has authenticated successfully. The argument must be M-bM-^@M-^\yesM-bM-^@M-^],
282 M-bM-^@M-^\delayedM-bM-^@M-^], or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\delayedM-bM-^@M-^].
285 This keyword can be followed by a list of group name patterns,
286 separated by spaces. Login is disallowed for users whose primary
287 group or supplementary group list matches one of the patterns.
288 Only group names are valid; a numerical group ID is not
289 recognized. By default, login is allowed for all groups. The
290 allow/deny directives are processed in the following order:
291 DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups.
293 See PATTERNS in ssh_config(5) for more information on patterns.
296 This keyword can be followed by a list of user name patterns,
297 separated by spaces. Login is disallowed for user names that
298 match one of the patterns. Only user names are valid; a
299 numerical user ID is not recognized. By default, login is
300 allowed for all users. If the pattern takes the form USER@HOST
301 then USER and HOST are separately checked, restricting logins to
302 particular users from particular hosts. The allow/deny
303 directives are processed in the following order: DenyUsers,
304 AllowUsers, DenyGroups, and finally AllowGroups.
306 See PATTERNS in ssh_config(5) for more information on patterns.
309 Specifies the hash algorithm used when logging key fingerprints.
310 Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^]. The default is M-bM-^@M-^\sha256M-bM-^@M-^].
313 Forces the execution of the command specified by ForceCommand,
314 ignoring any command supplied by the client and ~/.ssh/rc if
315 present. The command is invoked by using the user's login shell
316 with the -c option. This applies to shell, command, or subsystem
317 execution. It is most useful inside a Match block. The command
318 originally supplied by the client is available in the
319 SSH_ORIGINAL_COMMAND environment variable. Specifying a command
320 of M-bM-^@M-^\internal-sftpM-bM-^@M-^] will force the use of an in-process sftp
321 server that requires no support files when used with
325 Specifies whether remote hosts are allowed to connect to ports
326 forwarded for the client. By default, sshd(8) binds remote port
327 forwardings to the loopback address. This prevents other remote
328 hosts from connecting to forwarded ports. GatewayPorts can be
329 used to specify that sshd should allow remote port forwardings to
330 bind to non-loopback addresses, thus allowing other hosts to
331 connect. The argument may be M-bM-^@M-^\noM-bM-^@M-^] to force remote port
332 forwardings to be available to the local host only, M-bM-^@M-^\yesM-bM-^@M-^] to
333 force remote port forwardings to bind to the wildcard address, or
334 M-bM-^@M-^\clientspecifiedM-bM-^@M-^] to allow the client to select the address to
335 which the forwarding is bound. The default is M-bM-^@M-^\noM-bM-^@M-^].
338 Specifies whether user authentication based on GSSAPI is allowed.
339 The default is M-bM-^@M-^\noM-bM-^@M-^]. Note that this option applies to protocol
342 GSSAPICleanupCredentials
343 Specifies whether to automatically destroy the user's credentials
344 cache on logout. The default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that this option
345 applies to protocol version 2 only.
347 HostbasedAcceptedKeyTypes
348 Specifies the key types that will be accepted for hostbased
349 authentication as a comma-separated pattern list. The default
350 M-bM-^@M-^\*M-bM-^@M-^] will allow all key types. The -Q option of ssh(1) may be
351 used to list supported key types.
353 HostbasedAuthentication
354 Specifies whether rhosts or /etc/hosts.equiv authentication
355 together with successful public key client host authentication is
356 allowed (host-based authentication). This option is similar to
357 RhostsRSAAuthentication and applies to protocol version 2 only.
358 The default is M-bM-^@M-^\noM-bM-^@M-^].
360 HostbasedUsesNameFromPacketOnly
361 Specifies whether or not the server will attempt to perform a
362 reverse name lookup when matching the name in the ~/.shosts,
363 ~/.rhosts, and /etc/hosts.equiv files during
364 HostbasedAuthentication. A setting of M-bM-^@M-^\yesM-bM-^@M-^] means that sshd(8)
365 uses the name supplied by the client rather than attempting to
366 resolve the name from the TCP connection itself. The default is
367 M-bM-^@M-^\noM-bM-^@M-^].
370 Specifies a file containing a public host certificate. The
371 certificate's public key must match a private host key already
372 specified by HostKey. The default behaviour of sshd(8) is not to
373 load any certificates.
376 Specifies a file containing a private host key used by SSH. The
377 default is /etc/ssh/ssh_host_key for protocol version 1, and
378 /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key,
379 /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key for
380 protocol version 2. Note that sshd(8) will refuse to use a file
381 if it is group/world-accessible. It is possible to have multiple
382 host key files. M-bM-^@M-^\rsa1M-bM-^@M-^] keys are used for version 1 and M-bM-^@M-^\dsaM-bM-^@M-^],
383 M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^] or M-bM-^@M-^\rsaM-bM-^@M-^] are used for version 2 of the SSH
384 protocol. It is also possible to specify public host key files
385 instead. In this case operations on the private key will be
386 delegated to an ssh-agent(1).
389 Identifies the UNIX-domain socket used to communicate with an
390 agent that has access to the private host keys. If
391 M-bM-^@M-^\SSH_AUTH_SOCKM-bM-^@M-^] is specified, the location of the socket will be
392 read from the SSH_AUTH_SOCK environment variable.
395 Specifies that .rhosts and .shosts files will not be used in
396 RhostsRSAAuthentication or HostbasedAuthentication.
398 /etc/hosts.equiv and /etc/shosts.equiv are still used. The
399 default is M-bM-^@M-^\yesM-bM-^@M-^].
402 Specifies whether sshd(8) should ignore the user's
403 ~/.ssh/known_hosts during RhostsRSAAuthentication or
404 HostbasedAuthentication. The default is M-bM-^@M-^\noM-bM-^@M-^].
406 IPQoS Specifies the IPv4 type-of-service or DSCP class for the
407 connection. Accepted values are M-bM-^@M-^\af11M-bM-^@M-^], M-bM-^@M-^\af12M-bM-^@M-^], M-bM-^@M-^\af13M-bM-^@M-^], M-bM-^@M-^\af21M-bM-^@M-^],
408 M-bM-^@M-^\af22M-bM-^@M-^], M-bM-^@M-^\af23M-bM-^@M-^], M-bM-^@M-^\af31M-bM-^@M-^], M-bM-^@M-^\af32M-bM-^@M-^], M-bM-^@M-^\af33M-bM-^@M-^], M-bM-^@M-^\af41M-bM-^@M-^], M-bM-^@M-^\af42M-bM-^@M-^], M-bM-^@M-^\af43M-bM-^@M-^],
409 M-bM-^@M-^\cs0M-bM-^@M-^], M-bM-^@M-^\cs1M-bM-^@M-^], M-bM-^@M-^\cs2M-bM-^@M-^], M-bM-^@M-^\cs3M-bM-^@M-^], M-bM-^@M-^\cs4M-bM-^@M-^], M-bM-^@M-^\cs5M-bM-^@M-^], M-bM-^@M-^\cs6M-bM-^@M-^], M-bM-^@M-^\cs7M-bM-^@M-^], M-bM-^@M-^\efM-bM-^@M-^],
410 M-bM-^@M-^\lowdelayM-bM-^@M-^], M-bM-^@M-^\throughputM-bM-^@M-^], M-bM-^@M-^\reliabilityM-bM-^@M-^], or a numeric value.
411 This option may take one or two arguments, separated by
412 whitespace. If one argument is specified, it is used as the
413 packet class unconditionally. If two values are specified, the
414 first is automatically selected for interactive sessions and the
415 second for non-interactive sessions. The default is M-bM-^@M-^\lowdelayM-bM-^@M-^]
416 for interactive sessions and M-bM-^@M-^\throughputM-bM-^@M-^] for non-interactive
419 KbdInteractiveAuthentication
420 Specifies whether to allow keyboard-interactive authentication.
421 The argument to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default
422 is to use whatever value ChallengeResponseAuthentication is set
423 to (by default M-bM-^@M-^\yesM-bM-^@M-^]).
425 KerberosAuthentication
426 Specifies whether the password provided by the user for
427 PasswordAuthentication will be validated through the Kerberos
428 KDC. To use this option, the server needs a Kerberos servtab
429 which allows the verification of the KDC's identity. The default
430 is M-bM-^@M-^\noM-bM-^@M-^].
433 If AFS is active and the user has a Kerberos 5 TGT, attempt to
434 acquire an AFS token before accessing the user's home directory.
435 The default is M-bM-^@M-^\noM-bM-^@M-^].
437 KerberosOrLocalPasswd
438 If password authentication through Kerberos fails then the
439 password will be validated via any additional local mechanism
440 such as /etc/passwd. The default is M-bM-^@M-^\yesM-bM-^@M-^].
442 KerberosTicketCleanup
443 Specifies whether to automatically destroy the user's ticket
444 cache file on logout. The default is M-bM-^@M-^\yesM-bM-^@M-^].
447 Specifies the available KEX (Key Exchange) algorithms. Multiple
448 algorithms must be comma-separated. The supported algorithms
451 curve25519-sha256@libssh.org
452 diffie-hellman-group1-sha1
453 diffie-hellman-group14-sha1
454 diffie-hellman-group-exchange-sha1
455 diffie-hellman-group-exchange-sha256
462 curve25519-sha256@libssh.org,
463 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
464 diffie-hellman-group-exchange-sha256,
465 diffie-hellman-group14-sha1
467 The list of available key exchange algorithms may also be
468 obtained using the -Q option of ssh(1) with an argument of M-bM-^@M-^\kexM-bM-^@M-^].
470 KeyRegenerationInterval
471 In protocol version 1, the ephemeral server key is automatically
472 regenerated after this many seconds (if it has been used). The
473 purpose of regeneration is to prevent decrypting captured
474 sessions by later breaking into the machine and stealing the
475 keys. The key is never stored anywhere. If the value is 0, the
476 key is never regenerated. The default is 3600 (seconds).
479 Specifies the local addresses sshd(8) should listen on. The
480 following forms may be used:
482 ListenAddress host|IPv4_addr|IPv6_addr
483 ListenAddress host|IPv4_addr:port
484 ListenAddress [host|IPv6_addr]:port
486 If port is not specified, sshd will listen on the address and all
487 prior Port options specified. The default is to listen on all
488 local addresses. Multiple ListenAddress options are permitted.
489 Additionally, any Port options must precede this option for non-
490 port qualified addresses.
493 The server disconnects after this time if the user has not
494 successfully logged in. If the value is 0, there is no time
495 limit. The default is 120 seconds.
498 Gives the verbosity level that is used when logging messages from
499 sshd(8). The possible values are: QUIET, FATAL, ERROR, INFO,
500 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
501 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
502 higher levels of debugging output. Logging with a DEBUG level
503 violates the privacy of users and is not recommended.
505 MACs Specifies the available MAC (message authentication code)
506 algorithms. The MAC algorithm is used in protocol version 2 for
507 data integrity protection. Multiple algorithms must be comma-
508 separated. The algorithms that contain M-bM-^@M-^\-etmM-bM-^@M-^] calculate the MAC
509 after encryption (encrypt-then-mac). These are considered safer
510 and their use recommended. The supported MACs are:
521 hmac-md5-etm@openssh.com
522 hmac-md5-96-etm@openssh.com
523 hmac-ripemd160-etm@openssh.com
524 hmac-sha1-etm@openssh.com
525 hmac-sha1-96-etm@openssh.com
526 hmac-sha2-256-etm@openssh.com
527 hmac-sha2-512-etm@openssh.com
528 umac-64-etm@openssh.com
529 umac-128-etm@openssh.com
533 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
534 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
535 umac-64@openssh.com,umac-128@openssh.com,
536 hmac-sha2-256,hmac-sha2-512
538 The list of available MAC algorithms may also be obtained using
539 the -Q option of ssh(1) with an argument of M-bM-^@M-^\macM-bM-^@M-^].
541 Match Introduces a conditional block. If all of the criteria on the
542 Match line are satisfied, the keywords on the following lines
543 override those set in the global section of the config file,
544 until either another Match line or the end of the file. If a
545 keyword appears in multiple Match blocks that are satisfied, only
546 the first instance of the keyword is applied.
548 The arguments to Match are one or more criteria-pattern pairs or
549 the single token All which matches all criteria. The available
550 criteria are User, Group, Host, LocalAddress, LocalPort, and
551 Address. The match patterns may consist of single entries or
552 comma-separated lists and may use the wildcard and negation
553 operators described in the PATTERNS section of ssh_config(5).
555 The patterns in an Address criteria may additionally contain
556 addresses to match in CIDR address/masklen format, e.g.
557 M-bM-^@M-^\192.0.2.0/24M-bM-^@M-^] or M-bM-^@M-^\3ffe:ffff::/32M-bM-^@M-^]. Note that the mask length
558 provided must be consistent with the address - it is an error to
559 specify a mask length that is too long for the address or one
560 with bits set in this host portion of the address. For example,
561 M-bM-^@M-^\192.0.2.0/33M-bM-^@M-^] and M-bM-^@M-^\192.0.2.0/8M-bM-^@M-^] respectively.
563 Only a subset of keywords may be used on the lines following a
564 Match keyword. Available keywords are AcceptEnv,
565 AllowAgentForwarding, AllowGroups, AllowStreamLocalForwarding,
566 AllowTcpForwarding, AllowUsers, AuthenticationMethods,
567 AuthorizedKeysCommand, AuthorizedKeysCommandUser,
568 AuthorizedKeysFile, AuthorizedPrincipalsFile, Banner,
569 ChrootDirectory, DenyGroups, DenyUsers, ForceCommand,
570 GatewayPorts, GSSAPIAuthentication, HostbasedAcceptedKeyTypes,
571 HostbasedAuthentication, HostbasedUsesNameFromPacketOnly, IPQoS,
572 KbdInteractiveAuthentication, KerberosAuthentication,
573 MaxAuthTries, MaxSessions, PasswordAuthentication,
574 PermitEmptyPasswords, PermitOpen, PermitRootLogin, PermitTTY,
575 PermitTunnel, PermitUserRC, PubkeyAcceptedKeyTypes,
576 PubkeyAuthentication, RekeyLimit, RevokedKeys,
577 RhostsRSAAuthentication, RSAAuthentication, StreamLocalBindMask,
578 StreamLocalBindUnlink, TrustedUserCAKeys, X11DisplayOffset,
579 X11Forwarding and X11UseLocalHost.
582 Specifies the maximum number of authentication attempts permitted
583 per connection. Once the number of failures reaches half this
584 value, additional failures are logged. The default is 6.
587 Specifies the maximum number of open sessions permitted per
588 network connection. The default is 10.
591 Specifies the maximum number of concurrent unauthenticated
592 connections to the SSH daemon. Additional connections will be
593 dropped until authentication succeeds or the LoginGraceTime
594 expires for a connection. The default is 10:30:100.
596 Alternatively, random early drop can be enabled by specifying the
597 three colon separated values M-bM-^@M-^\start:rate:fullM-bM-^@M-^] (e.g. "10:30:60").
598 sshd(8) will refuse connection attempts with a probability of
599 M-bM-^@M-^\rate/100M-bM-^@M-^] (30%) if there are currently M-bM-^@M-^\startM-bM-^@M-^] (10)
600 unauthenticated connections. The probability increases linearly
601 and all connection attempts are refused if the number of
602 unauthenticated connections reaches M-bM-^@M-^\fullM-bM-^@M-^] (60).
604 PasswordAuthentication
605 Specifies whether password authentication is allowed. The
606 default is M-bM-^@M-^\yesM-bM-^@M-^].
609 When password authentication is allowed, it specifies whether the
610 server allows login to accounts with empty password strings. The
611 default is M-bM-^@M-^\noM-bM-^@M-^].
614 Specifies the destinations to which TCP port forwarding is
615 permitted. The forwarding specification must be one of the
619 PermitOpen IPv4_addr:port
620 PermitOpen [IPv6_addr]:port
622 Multiple forwards may be specified by separating them with
623 whitespace. An argument of M-bM-^@M-^\anyM-bM-^@M-^] can be used to remove all
624 restrictions and permit any forwarding requests. An argument of
625 M-bM-^@M-^\noneM-bM-^@M-^] can be used to prohibit all forwarding requests. By
626 default all port forwarding requests are permitted.
629 Specifies whether root can log in using ssh(1). The argument
630 must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\without-passwordM-bM-^@M-^], M-bM-^@M-^\forced-commands-onlyM-bM-^@M-^], or
631 M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\yesM-bM-^@M-^].
633 If this option is set to M-bM-^@M-^\without-passwordM-bM-^@M-^], password
634 authentication is disabled for root.
636 If this option is set to M-bM-^@M-^\forced-commands-onlyM-bM-^@M-^], root login with
637 public key authentication will be allowed, but only if the
638 command option has been specified (which may be useful for taking
639 remote backups even if root login is normally not allowed). All
640 other authentication methods are disabled for root.
642 If this option is set to M-bM-^@M-^\noM-bM-^@M-^], root is not allowed to log in.
645 Specifies whether tun(4) device forwarding is allowed. The
646 argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\point-to-pointM-bM-^@M-^] (layer 3), M-bM-^@M-^\ethernetM-bM-^@M-^]
647 (layer 2), or M-bM-^@M-^\noM-bM-^@M-^]. Specifying M-bM-^@M-^\yesM-bM-^@M-^] permits both
648 M-bM-^@M-^\point-to-pointM-bM-^@M-^] and M-bM-^@M-^\ethernetM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
650 Independent of this setting, the permissions of the selected
651 tun(4) device must allow access to the user.
654 Specifies whether pty(4) allocation is permitted. The default is
655 M-bM-^@M-^\yesM-bM-^@M-^].
657 PermitUserEnvironment
658 Specifies whether ~/.ssh/environment and environment= options in
659 ~/.ssh/authorized_keys are processed by sshd(8). The default is
660 M-bM-^@M-^\noM-bM-^@M-^]. Enabling environment processing may enable users to bypass
661 access restrictions in some configurations using mechanisms such
665 Specifies whether any ~/.ssh/rc file is executed. The default is
666 M-bM-^@M-^\yesM-bM-^@M-^].
669 Specifies the file that contains the process ID of the SSH
670 daemon. The default is /var/run/sshd.pid.
672 Port Specifies the port number that sshd(8) listens on. The default
673 is 22. Multiple options of this type are permitted. See also
677 Specifies whether sshd(8) should print the date and time of the
678 last user login when a user logs in interactively. The default
679 is M-bM-^@M-^\yesM-bM-^@M-^].
682 Specifies whether sshd(8) should print /etc/motd when a user logs
683 in interactively. (On some systems it is also printed by the
684 shell, /etc/profile, or equivalent.) The default is M-bM-^@M-^\yesM-bM-^@M-^].
687 Specifies the protocol versions sshd(8) supports. The possible
688 values are M-bM-^@M-^X1M-bM-^@M-^Y and M-bM-^@M-^X2M-bM-^@M-^Y. Multiple versions must be comma-
689 separated. The default is M-bM-^@M-^X2M-bM-^@M-^Y. Note that the order of the
690 protocol list does not indicate preference, because the client
691 selects among multiple protocol versions offered by the server.
692 Specifying M-bM-^@M-^\2,1M-bM-^@M-^] is identical to M-bM-^@M-^\1,2M-bM-^@M-^].
694 PubkeyAcceptedKeyTypes
695 Specifies the key types that will be accepted for public key
696 authentication as a comma-separated pattern list. The default
697 M-bM-^@M-^\*M-bM-^@M-^] will allow all key types. The -Q option of ssh(1) may be
698 used to list supported key types.
701 Specifies whether public key authentication is allowed. The
702 default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that this option applies to protocol
706 Specifies the maximum amount of data that may be transmitted
707 before the session key is renegotiated, optionally followed a
708 maximum amount of time that may pass before the session key is
709 renegotiated. The first argument is specified in bytes and may
710 have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate Kilobytes,
711 Megabytes, or Gigabytes, respectively. The default is between
712 M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher. The optional second
713 value is specified in seconds and may use any of the units
714 documented in the TIME FORMATS section. The default value for
715 RekeyLimit is M-bM-^@M-^\default noneM-bM-^@M-^], which means that rekeying is
716 performed after the cipher's default amount of data has been sent
717 or received and no time based rekeying is done. This option
718 applies to protocol version 2 only.
721 Specifies revoked public keys. Keys listed in this file will be
722 refused for public key authentication. Note that if this file is
723 not readable, then public key authentication will be refused for
724 all users. Keys may be specified as a text file, listing one
725 public key per line, or as an OpenSSH Key Revocation List (KRL)
726 as generated by ssh-keygen(1). For more information on KRLs, see
727 the KEY REVOCATION LISTS section in ssh-keygen(1).
729 RhostsRSAAuthentication
730 Specifies whether rhosts or /etc/hosts.equiv authentication
731 together with successful RSA host authentication is allowed. The
732 default is M-bM-^@M-^\noM-bM-^@M-^]. This option applies to protocol version 1 only.
735 Specifies whether pure RSA authentication is allowed. The
736 default is M-bM-^@M-^\yesM-bM-^@M-^]. This option applies to protocol version 1
740 Defines the number of bits in the ephemeral protocol version 1
741 server key. The minimum value is 512, and the default is 1024.
744 Sets the octal file creation mode mask (umask) used when creating
745 a Unix-domain socket file for local or remote port forwarding.
746 This option is only used for port forwarding to a Unix-domain
749 The default value is 0177, which creates a Unix-domain socket
750 file that is readable and writable only by the owner. Note that
751 not all operating systems honor the file mode on Unix-domain
754 StreamLocalBindUnlink
755 Specifies whether to remove an existing Unix-domain socket file
756 for local or remote port forwarding before creating a new one.
757 If the socket file already exists and StreamLocalBindUnlink is
758 not enabled, sshd will be unable to forward the port to the Unix-
759 domain socket file. This option is only used for port forwarding
760 to a Unix-domain socket file.
762 The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
765 Specifies whether sshd(8) should check file modes and ownership
766 of the user's files and home directory before accepting login.
767 This is normally desirable because novices sometimes accidentally
768 leave their directory or files world-writable. The default is
769 M-bM-^@M-^\yesM-bM-^@M-^]. Note that this does not apply to ChrootDirectory, whose
770 permissions and ownership are checked unconditionally.
773 Configures an external subsystem (e.g. file transfer daemon).
774 Arguments should be a subsystem name and a command (with optional
775 arguments) to execute upon subsystem request.
777 The command sftp-server(8) implements the M-bM-^@M-^\sftpM-bM-^@M-^] file transfer
780 Alternately the name M-bM-^@M-^\internal-sftpM-bM-^@M-^] implements an in-process
781 M-bM-^@M-^\sftpM-bM-^@M-^] server. This may simplify configurations using
782 ChrootDirectory to force a different filesystem root on clients.
784 By default no subsystems are defined. Note that this option
785 applies to protocol version 2 only.
788 Gives the facility code that is used when logging messages from
789 sshd(8). The possible values are: DAEMON, USER, AUTH, LOCAL0,
790 LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The
794 Specifies whether the system should send TCP keepalive messages
795 to the other side. If they are sent, death of the connection or
796 crash of one of the machines will be properly noticed. However,
797 this means that connections will die if the route is down
798 temporarily, and some people find it annoying. On the other
799 hand, if TCP keepalives are not sent, sessions may hang
800 indefinitely on the server, leaving M-bM-^@M-^\ghostM-bM-^@M-^] users and consuming
803 The default is M-bM-^@M-^\yesM-bM-^@M-^] (to send TCP keepalive messages), and the
804 server will notice if the network goes down or the client host
805 crashes. This avoids infinitely hanging sessions.
807 To disable TCP keepalive messages, the value should be set to
808 M-bM-^@M-^\noM-bM-^@M-^].
811 Specifies a file containing public keys of certificate
812 authorities that are trusted to sign user certificates for
813 authentication. Keys are listed one per line; empty lines and
814 comments starting with M-bM-^@M-^X#M-bM-^@M-^Y are allowed. If a certificate is
815 presented for authentication and has its signing CA key listed in
816 this file, then it may be used for authentication for any user
817 listed in the certificate's principals list. Note that
818 certificates that lack a list of principals will not be permitted
819 for authentication using TrustedUserCAKeys. For more details on
820 certificates, see the CERTIFICATES section in ssh-keygen(1).
822 UseDNS Specifies whether sshd(8) should look up the remote host name and
823 check that the resolved host name for the remote IP address maps
824 back to the very same IP address. The default is M-bM-^@M-^\noM-bM-^@M-^].
827 Specifies whether login(1) is used for interactive login
828 sessions. The default is M-bM-^@M-^\noM-bM-^@M-^]. Note that login(1) is never used
829 for remote command execution. Note also, that if this is
830 enabled, X11Forwarding will be disabled because login(1) does not
831 know how to handle xauth(1) cookies. If UsePrivilegeSeparation
832 is specified, it will be disabled after authentication.
834 UsePAM Enables the Pluggable Authentication Module interface. If set to
835 M-bM-^@M-^\yesM-bM-^@M-^] this will enable PAM authentication using
836 ChallengeResponseAuthentication and PasswordAuthentication in
837 addition to PAM account and session module processing for all
838 authentication types.
840 Because PAM challenge-response authentication usually serves an
841 equivalent role to password authentication, you should disable
842 either PasswordAuthentication or ChallengeResponseAuthentication.
844 If UsePAM is enabled, you will not be able to run sshd(8) as a
845 non-root user. The default is M-bM-^@M-^\noM-bM-^@M-^].
847 UsePrivilegeSeparation
848 Specifies whether sshd(8) separates privileges by creating an
849 unprivileged child process to deal with incoming network traffic.
850 After successful authentication, another process will be created
851 that has the privilege of the authenticated user. The goal of
852 privilege separation is to prevent privilege escalation by
853 containing any corruption within the unprivileged processes. The
854 default is M-bM-^@M-^\yesM-bM-^@M-^]. If UsePrivilegeSeparation is set to M-bM-^@M-^\sandboxM-bM-^@M-^]
855 then the pre-authentication unprivileged process is subject to
856 additional restrictions.
859 Optionally specifies additional text to append to the SSH
860 protocol banner sent by the server upon connection. The default
861 is M-bM-^@M-^\noneM-bM-^@M-^].
864 Specifies the first display number available for sshd(8)'s X11
865 forwarding. This prevents sshd from interfering with real X11
866 servers. The default is 10.
869 Specifies whether X11 forwarding is permitted. The argument must
870 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
872 When X11 forwarding is enabled, there may be additional exposure
873 to the server and to client displays if the sshd(8) proxy display
874 is configured to listen on the wildcard address (see
875 X11UseLocalhost below), though this is not the default.
876 Additionally, the authentication spoofing and authentication data
877 verification and substitution occur on the client side. The
878 security risk of using X11 forwarding is that the client's X11
879 display server may be exposed to attack when the SSH client
880 requests forwarding (see the warnings for ForwardX11 in
881 ssh_config(5)). A system administrator may have a stance in
882 which they want to protect clients that may expose themselves to
883 attack by unwittingly requesting X11 forwarding, which can
884 warrant a M-bM-^@M-^\noM-bM-^@M-^] setting.
886 Note that disabling X11 forwarding does not prevent users from
887 forwarding X11 traffic, as users can always install their own
888 forwarders. X11 forwarding is automatically disabled if UseLogin
892 Specifies whether sshd(8) should bind the X11 forwarding server
893 to the loopback address or to the wildcard address. By default,
894 sshd binds the forwarding server to the loopback address and sets
895 the hostname part of the DISPLAY environment variable to
896 M-bM-^@M-^\localhostM-bM-^@M-^]. This prevents remote hosts from connecting to the
897 proxy display. However, some older X11 clients may not function
898 with this configuration. X11UseLocalhost may be set to M-bM-^@M-^\noM-bM-^@M-^] to
899 specify that the forwarding server should be bound to the
900 wildcard address. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
901 default is M-bM-^@M-^\yesM-bM-^@M-^].
904 Specifies the full pathname of the xauth(1) program. The default
905 is /usr/X11R6/bin/xauth.
908 sshd(8) command-line arguments and configuration file options that
909 specify time may be expressed using a sequence of the form:
910 time[qualifier], where time is a positive integer value and qualifier is
911 one of the following:
913 M-bM-^_M-(noneM-bM-^_M-) seconds
920 Each member of the sequence is added together to calculate the total time
923 Time format examples:
925 600 600 seconds (10 minutes)
927 1h30m 1 hour 30 minutes (90 minutes)
931 Contains configuration data for sshd(8). This file should be
932 writable by root only, but it is recommended (though not
933 necessary) that it be world-readable.
939 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
940 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
941 de Raadt and Dug Song removed many bugs, re-added newer features and
942 created OpenSSH. Markus Friedl contributed the support for SSH protocol
943 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support
944 for privilege separation.
946 OpenBSD 5.7 February 20, 2015 OpenBSD 5.7
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