Why does Cygwin execute shell commands very slowly?

Question

Just tests a very simple command like:

while true; do bash -c "echo hello"; done

You will find how much slow the bash in Cygwin is. Does anybody know why?

It's a fresh install of cygwin 1.7 on win7.

thanks to Jared's testing idea, I modified the command to this(adds bash -c):

time for i in {1..10} ; do bash -c "echo Hello" ; done
Hello
...
real 0m7.711s //it's the problem
user 0m0.091s
sys 0m0.476s

Answer 1

How about excluding Cygwin paths from your antivirus software ?

Answer 2

Check your path. Referring a non-existant path or a very slow network share can cause the symptoms you are describing.

Answer 3

Below are 3 possible causes which I encountered. Of course, other problems not mentioned can also cause slow shell commands in Cygwin.

• If you have the option "Automatically detect settings" in "LAN Settings", Windows will use the WPAD protocol to discover the local HTTP proxy. First it will send a DHCP "Inform" request with option 252, then it will try a DNS lookup on "wpad". These 2 operations can take a few seconds to time-out.

• If the shell accesses some paths like /cygdrive/... , a NetBIOS name query will be executed, which can also take some time to time out.

• If the shell accesses some paths like //mypath/... , a NetBIOS name query will be executed, which can also take some time to time out.

Solutions :

• Disable "Automatically detect settings" in "LAN Settings" in the Windows "Internet Options" control panel.

• Add the following entry in %SystemRoot%\system32\drivers\etc\hosts :

127.0.0.1 localhost cygdrive wpad

• Make sure to avoid double slashes at the beginning of all paths.

Answer 4

Finally, I found the source - a service named "QQPCMgr RTP Service" running on my office computer, it's the real time protection service of "QQ PC Manager".

By disabling it, the time of the script in the question falls back to:

real    0m0.943s
user    0m0.105s
sys     0m0.231s

I have told the developers of QQPCMgr about this, hope they will find the reason.

This still much slower than Linux, but gets the same "real time" of other cygwin computers.

Thank you all!