-\versionid $Id: faq.but,v 1.17 2002/01/02 15:44:06 simon Exp $
+\versionid $Id: faq.but,v 1.54 2004/02/04 18:39:14 jacob Exp $
\A{faq} PuTTY FAQ
This FAQ is published on the PuTTY web site, and also provided as an
appendix in the manual.
+\H{faq-intro} Introduction
+
+\S{faq-what} What is PuTTY?
+
+PuTTY is a client program for the SSH, Telnet and Rlogin network
+protocols.
+
+These protocols are all used to run a remote session on a computer,
+over a network. PuTTY implements the client end of that session: the
+end at which the session is displayed, rather than the end at which
+it runs.
+
+In really simple terms: you run PuTTY on a Windows machine, and tell
+it to connect to (for example) a Unix machine. PuTTY opens a window.
+Then, anything you type into that window is sent straight to the
+Unix machine, and everything the Unix machine sends back is
+displayed in the window. So you can work on the Unix machine as if
+you were sitting at its console, while actually sitting somewhere
+else.
+
\H{faq-support} Features supported in PuTTY
In general, if you want to know if PuTTY supports a particular
development snapshots, in which case testing will be very welcome.
\b try the
-\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist.html}{Wishlist
+\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/}{Wishlist
page}, and see if you can find the feature there. If it's on there,
-it probably \e{hasn't} been implemented.
+and not in the \q{Recently fixed} section, it probably \e{hasn't} been
+implemented.
\S{faq-ssh2}{Question} Does PuTTY support SSH v2?
Yes. SSH v2 support has been available in PuTTY since version 0.50.
-However, currently the \e{default} SSH protocol is v1; to select SSH
-v2 if your server supports both, go to the SSH panel and change the
-\e{Preferred SSH protocol version} option.
-Public key authentication (both RSA and DSA) in SSH v2 has been
-added since version 0.51.
+Public key authentication (both RSA and DSA) in SSH v2 is new in
+version 0.52.
\S{faq-ssh2-keyfmt}{Question} Does PuTTY support reading OpenSSH or
\cw{ssh.com} SSHv2 private key files?
-Not at present. OpenSSH and \cw{ssh.com} have totally different
-formats for private key files, and neither one is particularly
-pleasant, so PuTTY has its own. We do plan to write a converter at
-some stage.
+PuTTY doesn't support this natively, but as of 0.53
+PuTTYgen can convert both OpenSSH and \cw{ssh.com} private key
+files into PuTTY's format.
\S{faq-ssh1}{Question} Does PuTTY support SSH v1?
\S{faq-localecho}{Question} Does PuTTY support local echo?
-Yes.
+Yes. Version 0.52 has proper support for local echo.
-In version 0.51 and before, local echo cannot be separated from
+In version 0.51 and before, local echo could not be separated from
local line editing (where you type a line of text locally, and it is
not sent to the server until you press Return, so you have the
chance to edit it and correct mistakes \e{before} the server sees
-it). The two features can be enabled and disabled from the Terminal
-panel, using the checkbox marked \q{Use local terminal line
-discipline}. Note that due to a bug in those versions of PuTTY,
-changing this feature in mid-session will have no effect; you have
-to enable it \e{before} you open the connection.
-
-In later versions, local echo and local line editing are separate
-options, and by default PuTTY will try to determine automatically
-whether to enable them or not, based on which protocol you have
-selected and also based on hints from the server. If you have a
-problem with PuTTY's default choice, you can force each option to be
-enabled or disabled as you choose. The controls are in the Terminal
-panel, in the section marked \q{Line discipline options}.
+it). New in version 0.52, local echo and local line editing are
+separate options, and by default PuTTY will try to determine
+automatically whether to enable them or not, based on which protocol
+you have selected and also based on hints from the server. If you
+have a problem with PuTTY's default choice, you can force each
+option to be enabled or disabled as you choose. The controls are in
+the Terminal panel, in the section marked \q{Line discipline
+options}.
\S{faq-disksettings}{Question} Does PuTTY support storing its
settings in a disk file?
\S{faq-fullscreen}{Question} Does PuTTY support full-screen mode,
like a DOS box?
-Not in the 0.51 release, but it has been added since then.
+Yes; this is a new feature in version 0.52.
\S{faq-password-remember}{Question} Does PuTTY have the ability to
remember my password so I don't have to type it every time?
ones will not. Adding an option to turn host key checking off
completely is the wrong solution and we will not do it.
+If you have host keys available in the common \c{known_hosts} format,
+we have a script called
+\W{http://cvs.tartarus.org/putty/contrib/kh2reg.py}\c{kh2reg.py}
+to convert them to a Windows .REG file, which can be installed ahead of
+time by double-clicking or using \c{REGEDIT}.
+
\S{faq-server}{Question} Will you write an SSH server for the PuTTY
suite, to go with the client?
have time, and we don't have motivation. The code is available if
anyone else wants to try it.
+\S{faq-pscp-ascii}{Question} Can PSCP or PSFTP transfer files in
+ASCII mode?
+
+Unfortunately not.
+
+Until recently, this was a limitation of the file transfer protocols:
+the SCP and SFTP protocols had no notion of transferring a file in
+anything other than binary mode. (This is still true of SCP.)
+
+The current draft protocol spec of SFTP proposes a means of
+implementing ASCII transfer. At some point PSCP/PSFTP may implement
+this proposal.
+
\H{faq-ports} Ports to other operating systems
The eventual goal is for PuTTY to be a multi-platform program, able
-to run on at least Windows, MacOS and Unix. Whether this will
-actually ever happen I have no idea, but it is the plan. A Mac port
-has been started, but is only half-finished and currently not moving
-very fast.
+to run on at least Windows, Mac OS and Unix.
Porting will become easier once PuTTY has a generalised porting
layer, drawing a clear line between platform-dependent and
-platform-independent code. The general intention is for this porting
-layer to evolve naturally as part of the process of doing the first
-port. One particularly nasty part of this will be separating the
-many configuration options into platform-dependent and
-platform-independent ones; for example, the options controlling when
-the Windows System menu appears will be pretty much meaningless
-under X11 or perhaps other windowing systems, whereas Telnet Passive
-Mode is universal and shouldn't need to be specified once for each
-platform.
-
-\S{faq-wince}{Question} Will there be a port to Windows CE?
-
-Probably not in the particularly near future. Despite sharing large
-parts of the Windows API, in practice WinCE doesn't appear to be
-significantly easier to port to than a totally different operating
-system.
-
-However, PuTTY on portable devices would clearly be a useful thing,
-so in the long term I hope there will be a WinCE port.
+platform-independent code. The general intention was for this
+porting layer to evolve naturally as part of the process of doing
+the first port; a Unix port is now under way and the plan seems to
+be working so far.
+
+\S{faq-ports-general}{Question} What ports of PuTTY exist?
+
+Currently, release versions of PuTTY only run on full Win32 systems.
+This includes Windows 95, 98, and ME, and it includes Windows NT,
+Windows 2000 and Windows XP. In the development code, partial ports
+to Unix (see \k{faq-unix}) and the Mac OS (see \k{faq-mac-port}).
+are under way.
+
+Currently PuTTY does \e{not} run on Windows CE (see \k{faq-wince}),
+and it does not quite run on the Win32s environment under Windows
+3.1 (see \k{faq-win31}).
+
+We do not have release-quality ports for any other systems at the
+present time. If anyone told you we had a Mac port, or an iPaq port,
+or any other port of PuTTY, they were mistaken. We don't.
+
+\S{faq-unix}{Question} Will there be a port to Unix?
+
+It's currently being worked on. If you look at the nightly source
+snapshots, you should find a \c{unix} subdirectory, which should
+build you Unix ports of Plink, PuTTY itself, PuTTYgen, PSCP, PSFTP,
+and also \c{pterm} - an \cw{xterm}-type program which supports the
+same terminal emulation as PuTTY. We do not yet have a Unix port of
+Pageant.
+
+\S{faq-wince}{Question} Will there be a port to Windows CE or PocketPC?
+
+It's currently being worked on, but it's only in its early stages yet,
+and certainly isn't yet useful. PuTTY on portable devices would
+clearly be a useful thing, so in the long term I hope it can be
+brought up to release quality.
\S{faq-win31}{Question} Is there a port to Windows 3.1?
\S{faq-mac-port}{Question} Will there be a port to the Mac?
-A Mac port was started once and is half-finished, but development
-has been static for some time and the main PuTTY code has moved on,
-so it's not clear how quickly development would resume even if
-developer effort were available.
-
-\S{faq-unix}{Question} Will there be a port to Unix?
-
-I hope so, if only so that I can have an \cw{xterm}-like program
-that supports exactly the same terminal emulation as PuTTY. If and
-when we do do a Unix port, it will have a local-terminal back end so
-it can be used like an \cw{xterm}, rather than only being usable as
-a network utility.
+There is a port to the Mac OS in progress. It's just about usable, but
+has an awful lot of gaps and rough edges that will need cleaning up
+before release.
\S{faq-epoc}{Question} Will there be a port to EPOC?
for, it might be a long time before any of us get round to learning
a new system and doing the port for that.
+However, some of the work has been done by other people, and a beta
+port of PuTTY for the Nokia 9200 Communicator series is available
+from \W{http://www.s2.org/putty/}\cw{http://www.s2.org/putty/}
+
\H{faq-embedding} Embedding PuTTY in other programs
\S{faq-dll}{Question} Is the SSH or Telnet code available as a DLL?
\S{faq-term}{Question} What terminal type does PuTTY use?
For most purposes, PuTTY can be considered to be an \cw{xterm}
-terminal, although full support for some of \cw{xterm}'s features,
-such as passing mouse actions to the server-side program, is not
-present in the 0.51 release (but has been added since).
+terminal.
PuTTY also supports some terminal control sequences not supported by
the real \cw{xterm}: notably the Linux console sequences that
create a Windows shortcut that invokes PuTTY with a command line
like
-\c \path\name\to\putty.exe @mysession
+\c \path\name\to\putty.exe -load mysession
+
+(Note: prior to 0.53, the syntax was \c{@session}. This is now
+deprecated and may be removed at some point.)
\S{faq-startssh}{Question} How can I start an SSH session straight
from the command line?
\S{faq-tunnels}{Question} How do I use X forwarding and port
forwarding? I can't find the Tunnels panel.
-If you're looking in the 0.51 release or earlier, the Tunnels panel
-isn't there. It was added in the development snapshots after 0.51,
-and releases 0.52 and onwards will contain it.
+This is a new feature in version 0.52. You should upgrade.
\S{faq-options}{Question} How do I use all PuTTY's features (public
-keys, port forwarding, SSH v2, etc.) in PSCP, PSFTP and Plink?
+keys, proxying, cipher selection, etc.) in PSCP, PSFTP and Plink?
-The command-line tools are currently rather short of command line
-options to enable this sort of thing. However, you can use most of
+Most major features (e.g., public keys, port forwarding) are available
+through command line options. See the documentation.
+
+Not all features are accessible from the command line yet, although
+we'd like to fix this. In the meantime, you can use most of
PuTTY's features if you create a PuTTY saved session, and then use
the name of the saved session on the command line in place of a
hostname. This works for PSCP, PSFTP and Plink (but don't expect
\S{faq-incorrect-mac}{Question} Why do I see \q{Incorrect MAC
received on packet}?
-This is due to a bug in old SSH 2 servers distributed by
-\cw{ssh.com}. Version 2.3.0 and below of their SSH 2 server
+One possible cause of this that used to be common is a bug in old
+SSH 2 servers distributed by \cw{ssh.com}. (This is not the only
+possible cause; see \k{errors-crc} in the documentation.)
+Version 2.3.0 and below of their SSH 2 server
constructs Message Authentication Codes in the wrong way, and
expects the client to construct them in the same wrong way. PuTTY
constructs the MACs correctly by default, and hence these old
servers will fail to work with it.
-If you are using PuTTY version 0.51 or below, go to the SSH panel
-and check the box labelled \q{Imitate SSH 2 MAC bug}. This will
-cause PuTTY to construct its MACs in the same incorrect manner as
-the buggy servers, so it will be able to work with them.
+If you are using PuTTY version 0.52 or better, this should work
+automatically: PuTTY should detect the buggy servers from their
+version number announcement, and automatically start to construct
+its MACs in the same incorrect manner as they do, so it will be able
+to work with them.
-Since version 0.51, PuTTY has been enhanced to detect buggy servers
-automatically (when they announce their version) and enable the
-workaround without the user needing to ask. Therefore you \e{should}
-never have to use this option again after 0.52, but it is still
-provided just in case another buggy server shows up.
+If you are using PuTTY version 0.51 or below, you can enable the
+workaround by going to the SSH panel and ticking the box labelled
+\q{Imitate SSH 2 MAC bug}. It's possible that you might have to do
+this with 0.52 as well, if a buggy server exists that PuTTY doesn't
+know about.
In this context MAC stands for Message Authentication Code. It's a
cryptographic term, and it has nothing at all to do with Ethernet
MAC (Media Access Control) addresses.
+\S{faq-pscp-protocol}{Question} Why do I see \q{Fatal: Protocol
+error: Expected control record} in PSCP?
+
+This happens because PSCP was expecting to see data from the server
+that was part of the PSCP protocol exchange, and instead it saw data
+that it couldn't make any sense of at all.
+
+This almost always happens because the startup scripts in your
+account on the server machine are generating output. This is
+impossible for PSCP, or any other SCP client, to work around. You
+should never use startup files (\c{.bashrc}, \c{.cshrc} and so on)
+which generate output in non-interactive sessions.
+
+This is not actually a PuTTY problem. If PSCP fails in this way,
+then all other SCP clients are likely to fail in exactly the same
+way. The problem is at the server end.
+
\S{faq-colours}{Question} I clicked on a colour in the Colours
panel, and the colour didn't change in my terminal.
repeated one hour after the start of the connection, and PuTTY will
get this wrong.
-The bug has been fixed since version 0.51, so upgrading to a later
-version or snapshot should solve the problem.
+Upgrade to version 0.52 or better and the problem should go away.
\S{faq-outofmem}{Question} After trying to establish an SSH 2
connection, PuTTY says \q{Out of memory} and dies.
server instead); but it doesn't necessarily mean you've actually run
out of memory.
+\S{faq-outofmem2}{Question} When attempting a file transfer, either
+PSCP or PSFTP says \q{Out of memory} and dies.
+
+This is almost always caused by your login scripts on the server
+generating output. PSCP or PSFTP will receive that output when they
+were expecting to see the start of a file transfer protocol, and
+they will attempt to interpret the output as file-transfer protocol.
+This will usually lead to an \q{out of memory} error for much the
+same reasons as given in \k{faq-outofmem}.
+
+This is a setup problem in your account on your server, \e{not} a
+PSCP/PSFTP bug. Your login scripts should \e{never} generate output
+during non-interactive sessions; secure file transfer is not the
+only form of remote access that will break if they do.
+
+On Unix, a simple fix is to ensure that all the parts of your login
+script that might generate output are in \c{.profile} (if you use a
+Bourne shell derivative) or \c{.login} (if you use a C shell).
+Putting them in more general files such as \c{.bashrc} or \c{.cshrc}
+is liable to lead to problems.
+
+\S{faq-psftp-slow}{Question} PSFTP transfers files much slower than PSCP.
+
+We believe this is because the SFTP and SSH2 protocols are less
+efficient at bulk data transfer than SCP and SSH1, because every
+block of data transferred requires an acknowledgment from the far
+end. It would in theory be possible to queue several blocks of data
+to get round this speed problem, but as yet we haven't done the
+coding. If you really want this fixed, feel free to offer to help.
+
\S{faq-bce}{Question} When I run full-colour applications, I see
areas of black space where colour ought to be.
\S{faq-altgr}{Question} I can't type characters that require the
AltGr key.
-In PuTTY version 0.51, the AltGr key was broken. The bug has been
-fixed since then.
+In PuTTY version 0.51, the AltGr key was broken. Upgrade to version
+0.52 or better.
\S{faq-idleout}{Question} My PuTTY sessions unexpectedly close after
they are idle for a while.
page} on the PuTTY website (also provided as \k{feedback} in the
manual), and follow the guidelines contained in that.
+\S{faq-openssh-bad-openssl}{Question} Since my SSH server was upgraded
+to OpenSSH 3.1p1/3.4p1, I can no longer connect with PuTTY.
+
+There is a known problem when OpenSSH has been built against an
+incorrect version of OpenSSL; the quick workaround is to configure
+PuTTY to use SSH protocol 2 and the Blowfish cipher.
+
+For more details and OpenSSH patches, see
+\W{http://bugzilla.mindrot.org/show_bug.cgi?id=138}{bug 138} in the
+OpenSSH BTS.
+
+This is not a PuTTY-specific problem; if you try to connect with
+another client you'll likely have similar problems. (Although PuTTY's
+default cipher differs from many other clients.)
+
+\e{OpenSSH 3.1p1:} configurations known to be broken (and symptoms):
+
+\b SSH 2 with AES cipher (PuTTY says "Assertion failed! Expression:
+(len & 15) == 0" in sshaes.c, or "Out of memory", or crashes)
+
+\b SSH 2 with 3DES (PuTTY says "Incorrect MAC received on packet")
+
+\b SSH 1 with Blowfish (PuTTY says "Incorrect CRC received on
+packet")
+
+\b SSH 1 with 3DES
+
+\e{OpenSSH 3.4p1:} as of 3.4p1, only the problem with SSH 1 and
+Blowfish remains. Rebuild your server, apply the patch linked to from
+bug 138 above, or use another cipher (e.g., 3DES) instead.
+
+\e{Other versions:} we occasionally get reports of the same symptom
+and workarounds with older versions of OpenSSH, although it's not
+clear the underlying cause is the same.
+
+\S{faq-ssh2key-ssh1conn}{Question} Why do I see "Couldn't load private
+key from ..."? Why can PuTTYgen load my key but not PuTTY?
+
+It's likely that you've generated an SSH protocol 2 key with PuTTYgen,
+but you're trying to use it in an SSH 1 connection. SSH1 and SSH2 keys
+have different formats, and (at least in 0.52) PuTTY's reporting of a
+key in the wrong format isn't optimal.
+
+To connect using SSH 2 to a server that supports both versions, you
+need to change the configuration from the default (see \k{faq-ssh2}).
+
+\S{faq-rh8-utf8}{Question} When I'm connected to a Red Hat Linux 8.0
+system, some characters don't display properly.
+
+A common complaint is that hyphens in man pages show up as a-acute.
+
+With release 8.0, Red Hat appear to have made UTF-8 the default
+character set. There appears to be no way for terminal emulators such
+as PuTTY to know this (as far as we know, the appropriate escape
+sequence to switch into UTF-8 mode isn't sent).
+
+A fix is to configure sessions to RH8 systems to use UTF-8
+translation - see \k{config-charset} in the documentation. (Note that
+if you use \q{Change Settings}, changes may not take place immediately
+- see \k{faq-resetterm}.)
+
+If you really want to change the character set used by the server, the
+right place is \c{/etc/sysconfig/i18n}, but this shouldn't be
+necessary.
+
\H{faq-secure} Security questions
\S{faq-publicpc}{Question} Is it safe for me to download PuTTY and
probably OK. However, if you have the choice, we still recommend you
use RSA instead.
+\S{faq-virtuallock}{Question} Couldn't Pageant use
+\cw{VirtualLock()} to stop private keys being written to disk?
+
+Unfortunately not. The \cw{VirtualLock()} function in the Windows
+API doesn't do a proper job: it may prevent small pieces of a
+process's memory from being paged to disk while the process is
+running, but it doesn't stop the process's memory as a whole from
+being swapped completely out to disk when the process is long-term
+inactive. And Pageant spends most of its time inactive.
+
\H{faq-admin} Administrative questions
\S{faq-domain}{Question} Would you like me to register you a nicer
There isn't one, that we know of.
-If someone else wants to set up a mailing list for PuTTY users to
-help each other with common problems, that would be fine with us;
-but the PuTTY team would almost certainly not have the time to read
-it, so any questions the list couldn't answer would have to be
-forwarded on to us by the questioner. In any case, it's probably
-better to use the established newsgroup \cw{comp.security.ssh} for
-this purpose.
+If someone else wants to set up a mailing list or other forum for
+PuTTY users to help each other with common problems, that would be
+fine with us, though the PuTTY team would almost certainly not have the
+time to read it. It's probably better to use the established
+newsgroup \cw{comp.security.ssh} for this purpose.
\S{faq-donations}{Question} How can I donate to PuTTY development?
you go to \W{http://www.e-gold.com}\cw{www.e-gold.com}, and deposit
your donation in account number 174769. Then send us e-mail to let
us know you've done so (otherwise we might not notice for months!).
+Alternatively, if e-gold isn't convenient for you, you can donate to
+\cw{<anakin@pobox.com>} using PayPal
+(\W{http://www.paypal.com/}\cw{www.paypal.com}).
Small donations (tens of dollars or tens of euros) will probably be
spent on beer or curry, which helps motivate our volunteer team to
continue doing this for the world. Larger donations will be spent on
something that actually helps development, if we can find anything
-(perhaps new hardware, or a copy of Windows 2000), but if we can't
+(perhaps new hardware, or a copy of Windows XP), but if we can't
find anything then we'll just distribute the money among the
developers. If you want to be sure your donation is going towards
something worthwhile, ask us first. If you don't like these terms,
feel perfectly free not to donate. We don't mind.
+\H{faq-misc} Miscellaneous questions
+
+\S{faq-openssh}{Question} Is PuTTY a port of OpenSSH, or based on
+OpenSSH?
+
+No, it isn't. PuTTY is almost completely composed of code written
+from scratch for PuTTY. The only code we share with OpenSSH is the
+detector for SSH1 CRC compensation attacks, written by CORE SDI S.A.
+
\S{faq-sillyputty}{Question} Where can I buy silly putty?
You're looking at the wrong web site; the only PuTTY we know about
buy from Crazy Aaron's Putty World, at
\W{http://www.puttyworld.com}\cw{www.puttyworld.com}.
-\S{faq-pronounce}{Question} How do I pronounce PuTTY?
+\S{faq-meaning}{Question} What does \q{PuTTY} mean?
+
+It's the name of a popular SSH and Telnet client. Any other meaning
+is in the eye of the beholder. It's been rumoured that \q{PuTTY}
+is the antonym of \q{\cw{getty}}, or that it's the stuff that makes your
+Windows useful, or that it's a kind of plutonium Teletype. We
+couldn't possibly comment on such allegations.
+
+\S{faq-pronounce}{Question} How do I pronounce \q{PuTTY}?
-Exactly like the normal word \q{putty}. Just like the stuff you put
-on window frames. (One of the reasons it's called PuTTY is because
-it makes Windows usable. :-)
+Exactly like the English word \q{putty}, which we pronounce
+/\u02C8{'}p\u028C{V}t\u026A{I}/.
projects / u / mdw / putty / blobdiff