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Applied Andrey's and my improvments to FAQ item 4.2, discussed on the main ML.

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Warren Young 2015-02-17 22:38:54 +00:00
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winsup/doc/ChangeLog
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@ -1,3 +1,9 @@
2015-02-17 Warren Young <warren@etr-usa.com>
* faq-using.xml (faq.using.startup-slow): Applied Andrey Repin's
improvements <anrdaemon@yandex.ru>, plus made a few minor ones
of my own.
2015-02-16 Corinna Vinschen <corinna@vinschen.de> 2015-02-16 Corinna Vinschen <corinna@vinschen.de>
* setup-files.xml (setup-files): Drop hint to set HOME in Windows * setup-files.xml (setup-files): Drop hint to set HOME in Windows

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winsup/doc/faq-using.xml
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@ -33,63 +33,121 @@ it to other missing DLLs and identify their containing packages, see
<question><para>Starting a new terminal window is slow. What's going on?</para></question> <question><para>Starting a new terminal window is slow. What's going on?</para></question>
<answer> <answer>
<para>There are many possible causes for this. This answer is more a <para>There are many possible causes for this.</para>
list of things to look into than a set of solutions.</para>
<para>If your terminal windows suddenly began starting slowly after a
Cygwin upgrade, it may indicate issues in the authentication
setup.</para>
<para>For almost all its lifetime, Cygwin has used Unix-like
<filename>/etc/passwd</filename> and <filename>/etc/group</filename>
files to mirror the contents of the Windows SAM and AD databases.
Although these files can still be used, since Cygwin 1.7.34, new
installations now use the SAM/AD databases directly.</para>
<para>To switch to the new method, move these two files out of the way
and restart the Cygwin terminal. That runs Cygwin in its new default
mode.</para>
<para>If you are on a system that isn't using AD domain logins, this
makes Cygwin use the native Windows SAM database directly, which may be
faster than the old method involving <filename>/etc/passwd</filename>
and such. At worst, it will only be a bit slower. (The speed difference
you see depends on which benchmark you run.) For the AD case, it can be
slower than the old method, since it is trading a local file read for a
network request. Version 1.7.35 will reduce the number of AD server
requests the DLL makes relative to 1.7.34, with the consequence that you
will now have to alter <filename>/etc/nsswitch.conf</filename> in order
to change your Cygwin home directory, instead of being able to change it
from the AD configuration.</para>
<para>If you are still experiencing very slow shell startups, there are
a number of other things you can look into:</para>
<orderedlist> <orderedlist>
<listitem> <listitem>
<para>If your terminal windows suddenly began starting slowly after a <para>One common cause of slow Cygwin Terminal starts is a bad DNS
Cygwin upgrade, the most likely cause is that you have an outdated setup. This particularly affects AD clients, but there may be other
authentication setup.</para> things in your Cygwin startup that depend on getting fast answers
back from a network server.</para>
<para>For almost all its lifetime, Cygwin has used Unix-like <para>Keep in mind that this may affect Cygwin even when the domain
<filename>/etc/passwd</filename> and <filename>/etc/group</filename> files controller is on the same machine as Cygwin, or is on a nearby
to mirror the contents of the Windows SAM and AD databases. Although these server. A bad DNS server IP can cause long delays while the local
files can still be used, since Cygwin 1.7.34, new installations now use the TCP/IP stack times out on a connection to a server that simply isn't
SAM/AD databases directly.</para> there, for example.</para>
<para>To switch to the new method, move these two files out of the way and
restart the Cygwin terminal. That runs Cygwin in its new default mode. If
you are on a system that isn't using AD domain logins, this makes Cygwin
use the native Windows SAM database directly, which may be faster than the
old method involving <filename>/etc/passwd</filename> and such. At worst,
it will only be a bit slower. (Which situation applies depends on the
benchmark you run.)</para>
<para>If you are on an AD system, a hybrid approach you might consider is
to re-run <command>mkpasswd</command> and <command>mkgroup</command>, then
put the following into <filename>/etc/nsswitch.conf</filename> to make
Cygwin treat these files as read-only local caches of your AD database:
</para>
<screen>
passwd: files
group: files
</screen>
<para>By leaving out the "db" option, we are telling the Cygwin DLL not to
even <emphasis>try</emphasis> to do AD lookups. If your AD servers are
slow, this local cache will speed things up. The downside is the old stale
cache problem: any time the AD databases change, your local cache will go
out of date until you update the files manually.</para>
</listitem> </listitem>
<listitem> <listitem>
<para>Another common cause of slow Cygwin Terminal starts is a bad DNS <para>Another cause for AD client system is slow DC replies,
setup. Many things that occur during a Cygwin Terminal startup require commonly observed in configurations with remote DC access. The
fast DNS lookups.</para> Cygwin DLL queries information about every group you're in to
populate the local cache on startup. You may speed up this process a
little by caching your own information in local files. Run these
commands in a Cygwin terminal with write access to
<filename>/etc</filename>:</para>
<screen>getent passwd $(id -u) > /etc/passwd
getent group $(id -G) > /etc/group</screen>
<para>Also, set <filename>/etc/nsswitch.conf</filename> as
follows:</para>
<screen>passwd: files db
group: files db</screen>
<para>This will limit the need for Cygwin to contact the AD domain
controller (DC) while still allowing for additional information to
be retrieved from DC, such as when listing remote
directories.</para>
</listitem>
<listitem>
<para>Either in addition to the previous item or instead of it, you
can run <ulink
url="https://cygwin.com/cygwin-ug-net/using-cygserver.html"><command>cygserver</command></ulink>
as a local caching service to speed up DC requests.</para>
<para>Cygwin programs will check with <command>cygserver</command>
before trying to query the DC directly.</para>
</listitem>
<listitem>
<para>A less preferable option is to create a static read-only cache
of the authentication data. This is the old-fashioned method of
making Cygwin integrate with AD, the only method available in
releases before 1.7.34. To do this, run <command>mkpasswd</command>
and <command>mkgroup</command>, then put the following into
<filename>/etc/nsswitch.conf</filename> to make Cygwin treat these
files as the only sources of user and group information:</para>
<screen>passwd: files
group: files</screen>
<para>By leaving out the <computeroutput>db</computeroutput> option,
we are telling the Cygwin DLL not to even try to do AD lookups. If
your AD servers are slow, this local cache will speed things up. The
downside is that you open yourself up to the <ulink
url="http://en.wikipedia.org/wiki/Cache_(computing)">stale cache
problem</ulink>: any time the AD databases change, your local cache
will go out of date until you update the files manually.</para>
</listitem> </listitem>
</orderedlist> </orderedlist>
<para>If none of the above helps, the best troubleshooting method is to run <para>If none of the above helps, the best troubleshooting method is to
your startup scripts in debug mode. Right-click your Cygwin Terminal icon, go run your startup scripts in debug mode. Right-click your Cygwin Terminal
to Properties, and edit the command. It should be something like icon, go to Properties, and edit the command. It should be something
<command>C:\cygwin\bin\mintty.exe -i /Cygwin-Terminal.ico -</command>. like <command>C:\cygwin\bin\mintty.exe -i /Cygwin-Terminal.ico
Assuming you are using Bash for your login shell, change it to -</command>. Assuming you are using Bash for your login shell, change
<command>C:\cygwin64\bin\mintty /bin/bash -lx</command>. That will cause it to it to <command>C:\cygwin\bin\mintty /bin/bash -lx</command> then try
write out a line for every command it runs. A slow Cygwin Terminal launch running Cygwin Terminal again. The <option>-x</option> option tells Bash
usually means one or more of the many commands Cygwin runs when starting up to write every command it runs to the terminal before launching it. If
will take a long time. That will be your clue as to what's going on.</para> the terminal immediately starts filling with lines of text but then
pauses, the line where the output paused is your clue as to what's going
on. The Cygwin DLL proper probably isn't the cause of the slowdown in
this case, since those delays happen before the first line of text
appears in the terminal.</para>
</answer></qandaentry> </answer></qandaentry>
<qandaentry id="faq.using.slow"> <qandaentry id="faq.using.slow">