CODEWITHSUNDEEP
cgdb
graffo
graffo

Reputation: 51

running gdb on a web server

Using gdb, I am trying to trace the function calls of a web server. I set breakpoints on every function call and when I tell gdb to 'run' it breaks at all the right places while the server starts up. Then gdb says 'Program ended with code 01' and doesn't stop at breakpoints anymore (obviously). However, the web server is still running.

I want to be able to trace the function calls made on an incoming HTTP request, so just breaking during server startup is useless to me.

Is there some trick to using gdb when tracing a daemon server so that it doesn't just end like above?

Upvotes: 5

Views: 672

Answers (2)

President James K. Polk
President James K. Polk

Reputation: 41967

set follow-fork-mode child

see https://sourceware.org/gdb/onlinedocs/gdb/Forks.html for example

From the link:

If you want to follow the child process instead of the parent process, use the command set follow-fork-mode.

set follow-fork-mode mode Set the debugger response to a program call of fork or vfork. A call to fork or vfork creates a new process. The mode argument can be:

parent The original process is debugged after a fork. The child process runs unimpeded. This is the default.

child The new process is debugged after a fork. The parent process runs unimpeded.

show follow-fork-mode Display the current debugger response to a fork or vfork call.

Upvotes: 1

Employed Russian
Employed Russian

Reputation: 213576

You didn't say which server you are trying to trace, but likely it is Apache.

Detailed instructions are here. Note the -X command line argument, which prevents httpd from forking children.

Also note that the instructions are the first result for this search.

Upvotes: 2

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