dropbear(8) System Manager's Manual dropbear(8)
NAME
dropbear - lightweight SSH2 server
SYNOPSIS
dropbear [-FEmwsgjki] [-b banner] [-d dsskey] [-r rsakey] [-p [address:]port]
DESCRIPTION
dropbear is a SSH 2 server designed to be small enough to be used in small memory environments, while still being functional and secure
enough for general use.
OPTIONS
-b banner
bannerfile. Display the contents of the file banner before user login (default: none).
-d dsskey
dsskeyfile. Use the contents of the file dsskey for the DSS host key (default: /etc/dropbear/dropbear_dss_host_key). Note that
some SSH implementations use the term "DSA" rather than "DSS", they mean the same thing. This file is generated with dropbear-
key(8).
-r rsakey
rsakeyfile. Use the contents of the file rsakey for the rsa host key (default: /etc/dropbear/dropbear_rsa_host_key). This file is
generated with dropbearkey(8).
-F Don't fork into background.
-E Log to standard error rather than syslog.
-m Don't display the message of the day on login.
-w Disallow root logins.
-s Disable password logins.
-g Disable password logins for root.
-j Disable local port forwarding.
-k Disable remote port forwarding.
-p [address:]port
Listen on specified address and TCP port. If just a port is given listen on all addresses. up to 10 can be specified (default 22
if none specified).
-i Service program mode. Use this option to run dropbear under TCP/IP servers like inetd, tcpsvd, or tcpserver. In program mode the
-F option is implied, and -p options are ignored.
-P pidfile
Specify a pidfile to create when running as a daemon. If not specified, the default is /var/run/dropbear.pid
-a Allow remote hosts to connect to forwarded ports.
-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.
-I idle_timeout
Disconnect the session if no traffic is transmitted or received for idle_timeout seconds.
FILES
Authorized Keys
~/.ssh/authorized_keys can be set up to allow remote login with a RSA or DSS key. Each line is of the form
[restrictions] ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIgAsp... [comment]
and can be extracted from a Dropbear private host key with "dropbearkey -y". This is the same format as used by OpenSSH, though the
restrictions are a subset (keys with unknown restrictions are ignored). Restrictions are comma separated, with double quotes around
spaces in arguments. Available restrictions are:
no-port-forwarding
Don't allow port forwarding for this connection
no-agent-forwarding
Don't allow agent forwarding for this connection
no-X11-forwarding
Don't allow X11 forwarding for this connection
no-pty Disable PTY allocation. Note that a user can still obtain most of the same functionality with other means even if no-pty is set.
command="forced_command"
Disregard the command provided by the user and always run forced_command.
The authorized_keys file and its containing ~/.ssh directory must only be writable by the user, otherwise Dropbear will not allow a
login using public key authentication.
Host Key Files
Host key files are read at startup from a standard location, by default /etc/dropbear/dropbear_dss_host_key and /etc/dropbear/drop-
bear_rsa_host_key or specified on the commandline with -d or -r. These are of the form generated by dropbearkey.
Message Of The Day
By default the file /etc/motd will be printed for any login shell (unless disabled at compile-time). This can also be disabled per-
user by creating a file ~/.hushlogin .
ENVIRONMENT VARIABLES
Dropbear sets the standard variables USER, LOGNAME, HOME, SHELL, PATH, and TERM.
The variables below are set for sessions as appropriate.
SSH_TTY
This is set to the allocated TTY if a PTY was used.
SSH_CONNECTION
Contains "<remote_ip> <remote_port> <local_ip> <local_port>".
DISPLAY
Set X11 forwarding is used.
SSH_ORIGINAL_COMMAND
If a 'command=' authorized_keys option was used, the original command is specified in this variable. If a shell was requested this
is set to an empty value.
SSH_AUTH_SOCK
Set to a forwarded ssh-agent connection.
AUTHOR
Matt Johnston (matt@ucc.asn.au).
Gerrit Pape (pape@smarden.org) wrote this manual page.
SEE ALSO
dropbearkey(8), dbclient(1)
http://matt.ucc.asn.au/dropbear/dropbear.html
dropbear(8)