dropbear - lightweight SSH server
[ flag arguments
] [-b banner]
[-p [ address:]port]
is a small SSH server
- -b banner
- bannerfile. Display the contents of the file banner
before user login (default: none).
- -r hostkey
- Use the contents of the file hostkey for the SSH
hostkey. This file is generated with dropbearkey(1) or
automatically with the '-R' option. See "Host Key Files"
- Generate hostkeys automatically. See "Host Key
- Don't fork into background.
- Log to standard error rather than syslog.
- Don't display the message of the day on login.
- Disallow root logins.
- Disable password logins.
- Disable password logins for root.
- Disable local port forwarding.
- 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).
- 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
- 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. 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.
- Print the version
- Authorized Keys
~/.ssh/authorized_keys can be set up to allow remote login with a RSA,
ECDSA, or DSS key. Each line is of the form
- [restrictions] ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIgAsp...
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:
- Don't allow port forwarding for this connection
- Don't allow agent forwarding for this connection
- Don't allow X11 forwarding for this connection
- Disable PTY allocation. Note that a user can still obtain
most of the same functionality with other means even if no-pty is set.
- Disregard the command provided by the user and always run
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
and /etc/dropbear/dropbear_ecdsa_host_key or specified on the commandline
with -r. These are of the form generated by dropbearkey. The -R option can
be used to automatically generate keys in the default location - keys will
be generated after startup when the first connection is established. This
had the benefit that the system /dev/urandom random number source has a
better chance of being securely seeded.
- 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 .
Dropbear sets the standard variables USER, LOGNAME, HOME, SHELL, PATH, and TERM.
The variables below are set for sessions as appropriate.
- This is set to the allocated TTY if a PTY was used.
- Contains "<remote_ip> <remote_port>
- Set X11 forwarding is used.
- 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.
- Set to a forwarded ssh-agent connection.
Dropbear only supports SSH protocol version 2.
Matt Johnston (firstname.lastname@example.org).
Gerrit Pape (email@example.com) wrote this manual page.
dropbearkey(1), dbclient(1), dropbearconvert(1)