Ubuntu Manpage: dbclient - lightweight SSH client

Provided by: dropbear-bin_2019.78-2build1_amd64

NAME

       dbclient - lightweight SSH client

SYNOPSIS

       dbclient  [flag  arguments]  [-p  port]  [-i  id]  [-L  l:h:p]  [-R  l:h:p] [-l user] host
       [more flags] [command]

       dbclient [args] [user1]@host1[^port1],[user2]@host2[^port2],...

DESCRIPTION

       dbclient is a small SSH client

OPTIONS

command
A command to run on the remote host. This will normally be run by the remote host
using the user's shell. The command begins at the first hyphen argument after the
host argument. If no command is specified an interactive terminal will be opened
(see -t and -T).

-p port
Connect to port on the remote host. Alternatively a port can be specified as
hostname^port. Default is 22.

-i idfile
Identity file. Read the identity key from file idfile (multiple allowed). This
file is created with dropbearkey(1) or converted from OpenSSH with
dropbearconvert(1). The default path ~/.ssh/id_dropbear is used

-L [listenaddress]:listenport:host:port
Local port forwarding. Forward the port listenport on the local host through the
SSH connection to port port on the host host.

-R [listenaddress]:listenport:host:port
Remote port forwarding. Forward the port listenport on the remote host through the
SSH connection to port port on the host host.

-l user
Username. Login as user on the remote host.

-t Allocate a PTY. This is the default when no command is given, it gives a full
interactive remote session. The main effect is that keystrokes are sent remotely
immediately as opposed to local line-based editing.

-T Don't allocate a PTY. This is the default a command is given. See -t.

-N Don't request a remote shell or run any commands. Any command arguments are
ignored.

-f Fork into the background after authentication. A command argument (or -N) is
required. This is useful when using password authentication.

-g Allow non-local hosts to connect to forwarded ports. Applies to -L and -R forwarded
ports, though remote connections to -R forwarded ports may be limited by the ssh
server.

-y Always accept hostkeys if they are unknown. If a hostkey mismatch occurs the
connection will abort as normal. If specified a second time no host key checking is
performed at all, this is usually undesirable.

-A Forward agent connections to the remote host. dbclient will use any OpenSSH-style
agent program if available ($SSH_AUTH_SOCK will be set) for public key
authentication. Forwarding is only enabled if -A is specified.

-W windowsize
Specify the per-channel receive window buffer size. Increasing this may improve
network performance at the expense of memory use. Use -h to see the default buffer
size.

-K timeout_seconds
Ensure that traffic is transmitted at a certain interval in seconds. This is useful
for working around firewalls or routers that drop connections after a certain
period of inactivity. The trade-off is that a session may be closed if there is a
temporary lapse of network connectivity. A setting if 0 disables keepalives. If no
response is received for 3 consecutive keepalives the connection will be closed.

-I idle_timeout
Disconnect the session if no traffic is transmitted or received for idle_timeout
seconds.

-J proxy_command

-J &fd
Use the standard input/output of the program proxy_command rather than using a
normal TCP connection. A hostname should be still be provided, as this is used for
comparing saved hostkeys. This command will be executed as "exec proxy_command ..."
with the default shell.

The second form &fd will make dbclient use the numeric file descriptor as a socket.
This can be used for more complex tunnelling scenarios. Example usage with socat is

socat EXEC:'dbclient -J &38 ev',fdin=38,fdout=38 TCP4:host.example.com:22

-B endhost:endport
"Netcat-alike" mode, where Dropbear will connect to the given host, then create a
forwarded connection to endhost. This will then be presented as dbclient's standard
input/output.

-c cipherlist
Specify a comma separated list of ciphers to enable. Use -c help to list
possibilities.

-m MAClist
Specify a comma separated list of authentication MACs to enable. Use -m help to
list possibilities.

-o option
Can be used to give options in the format used by OpenSSH config file. This is
useful for specifying options for which there is no separate command-line flag.
For full details of the options listed below, and their possible values, see
ssh_config(5). The following options have currently been implemented:

ExitOnForwardFailure
Specifies whether dbclient should terminate the connection if it cannot set
up all requested local and remote port forwardings. The argument must be
“yes” or “no”. The default is “no”.

UseSyslog
Send dbclient log messages to syslog in addition to stderr.

-s The specified command will be requested as a subsystem, used for sftp. Dropbear
doesn't implement sftp itself but the OpenSSH sftp client can be used eg sftp -S
dbclient user@host

-b [address][:port]
Bind to a specific local address when connecting to the remote host. This can be
used to choose from multiple outgoing interfaces. Either address or port (or both)
can be given.

-V Print the version

MULTI-HOP

       Dropbear will also allow multiple "hops" to be specified, separated  by  commas.  In  this
       case  a connection will be made to the first host, then a TCP forwarded connection will be
       made through that to the second host, and so on. Hosts other than  the  final  destination
       will  not  see  anything  other  than  the encrypted SSH stream.  A port for a host can be
       specified with a caret (eg matt@martello^44 ).  This syntax can also be used with  scp  or
       rsync  (specifying  dbclient  as  the  ssh/rsh  command).  A file can be "bounced" through
       multiple SSH hops, eg

       scp -S dbclient matt@martello,root@wrt,canyons:/tmp/dump .

       Note that hostnames are resolved by the prior hop (so "canyons" would be resolved  by  the
       host  "wrt")  in the example above, the same way as other -L TCP forwarded hosts are. Host
       keys are checked locally based on the given hostname.

ESCAPE CHARACTERS

       Typing a newline  followed  by  the   key  sequence  ~.  (tilde,  dot)  will  terminate  a
       connection.   The  sequence  ~^Z  (tilde,  ctrl-z)  will  background  the connection. This
       behaviour only applies when a PTY is used.

ENVIRONMENT

       DROPBEAR_PASSWORD
              A password to use for remote authentication can be  specified  in  the  environment
              variable  DROPBEAR_PASSWORD.  Care should be taken that the password is not exposed
              to other users on a multi-user system, or stored in accessible files.

       SSH_ASKPASS
              dbclient  can  use  an  external  program  to  request  a  password  from  a  user.
              SSH_ASKPASS  should  be set to the path of a program that will return a password on
              standard output. This program will only be  used  if  either  DISPLAY  is  set  and
              standard input is not a TTY, or the environment variable SSH_ASKPASS_ALWAYS is set.

NOTES

       If  compiled  with  zlib  support  and if the server supports it, dbclient will always use
       compression.

AUTHOR

       Matt Johnston (matt@ucc.asn.au).
       Mihnea Stoenescu wrote initial Dropbear client support
       Gerrit Pape (pape@smarden.org) wrote this manual page.