Question has been asked before and I see bug report on ddd newsgroups but none of the suggested solutions work for me.
It comes up but when you try doing anything like opening a file it hangs with the message "waiting until GDB gets ready."
A crucial fact, reported by others too, is that it works fine for some users and not others. I've compared the environments and can't find any significant differences. Any suggestions will be most appreciated.
Answer
Encountered this problem too. The easy solution as posted above is to delete the init file in the ~/.ddd/ directory.
But that means all your customizations will be gone. So I started hunting for the real cause. I observed that the problem only occurs after I have used the "GDB Settings" dialog. Once you opened this dialog the init file mentioned above will grow because a lot of gdb settings will be stored there.
After shrinking those additional lines step by step I found the "offending line". The problem is caused by the setting for extended-prompt. After opening the GDB settings dialog this line will read like
set extended-prompt not set\n\
This "not set" is what gdb will report on "show extended-prompt". Unfortunatley "set extended-prompt is sort of buggy in gdb, so if I enter "set extended-prompt not set" in a gdb running from a shell without ddd involved gdb will lockup as well.
It looks like the only safe way of setting the extend-prompt is when it contains the string "(gdb)". So I modified the offending line in the init file and now it reads like this:
set extended-prompt (gdb) \n\
With this setting I do not encounter the problem any longer. Hope that helps in your case too.