SSHPASS(1) Sshpass User Manual SSHPASS(1)NAMEsshpass - noninteractive ssh password provider
SYNOPSISsshpass [-ffilename|-dnum|-ppassword|-e] [options] command arguments
DESCRIPTION
This manual page documents the sshpass command.
sshpass is a utility designed for running ssh using the mode referred
to as "keyboard-interactive" password authentication, but in non-inter‐
active mode.
ssh uses direct TTY access to make sure that the password is indeed
issued by an interactive keyboard user. Sshpass runs ssh in a dedicated
tty, fooling it into thinking it is getting the password from an inter‐
active user.
The command to run is specified after sshpass' own options. Typically
it will be "ssh" with arguments, but it can just as well be any other
command. The password prompt used by ssh is, however, currently hard‐
coded into sshpass.
Options
If no option is given, sshpass reads the password from the standard
input. The user may give at most one alternative source for the pass‐
word:
-ppassword
The password is given on the command line. Please note the sec‐
tion titled "SECURITY CONSIDERATIONS".
-ffilename
The password is the first line of the file filename.
-dnumber
number is a file descriptor inherited by sshpass from the run‐
ner. The password is read from the open file descriptor.
-e The password is taken from the environment variable "SSHPASS".
SECURITY CONSIDERATIONS
First and foremost, users of sshpass should realize that ssh's insis‐
tance on only getting the password interactively is not without reason.
It is close to impossible to securely store the password, and users of
sshpass should consider whether ssh's public key authentication pro‐
vides the same end-user experience, while involving less hassle and
being more secure.
The -p option should be considered the least secure of all of sshpass's
options. All system users can see the password in the command line
with a simple "ps" command. Sshpass makes a minimal attempt to hide the
password, but such attempts are doomed to create race conditions with‐
out actually solving the problem. Users of sshpass are encouraged to
use one of the other password passing techniques, which are all more
secure.
In particular, people writing programs that are meant to communicate
the password programatically are encouraged to use an anonymous pipe
and pass the pipe's reading end to sshpass using the -d option.
RETURN VALUES
As with any other program, sshpass returns 0 on success. In case of
failure, the following return codes are used:
1 Invalid command line argument
2 Conflicting arguments given
3 General runtime error
4 Unrecognized response from ssh (parse error)
5 Invalid/incorrect password
6 Host public key is unknown. sshpass exits without confirming the
new key.
In addition, ssh might be complaining about a man in the middle attack.
This complaint does not go to the tty. In other words, even with ssh‐
pass, the error message from ssh is printed to standard error. In such
a case ssh's return code is reported back. This is typically an unimag‐
inative (and non-informative) "255" for all error cases.
EXAMPLES
Run rsync over SSH using password authentication, passing the password
on the command line:
rsync --rsh='sshpass -p 12345 ssh -l test' host.example.com:path .
To do the same from a bourne shell script in a marginally less exposed
way:
SSHPASS=12345 rsync --rsh='sshpass -e ssh -l test' host.exam‐
ple.com:path .
BUGS
Sshpass is in its infancy at the moment. As such, bugs are highly pos‐
sible. In particular, if the password is read from stdin (no password
option at all), it is possible that some of the input aimed to be
passed to ssh will be read by sshpass and lost.
Sshpass utilizes the pty(7) interface to control the TTY for ssh. This
interface, at least on Linux, has a misfeature where if no slave file
descriptors are open, the master pty returns EIO. This is the normal
behavior, except a slave pty may be born at any point by a program
opening /dev/tty. This makes it impossible to reliably wait for events
without consuming 100% of the CPU.
Over the various versions different approaches were attempted at solv‐
ing this problem. Any given version of sshpass is released with the
belief that it is working, but experience has shown that these things
do, occasionally, break. This happened with OpenSSH version 5.6. As of
this writing, it is believed that sshpass is, again, working properly.
Lingnu Open Source Consulting August 6, 2011 SSHPASS(1)
