In qemudStartVMDaemon in/out/err for the virCommand are set based on FDs this results in a segfault in virCommandRun here VIR_DEBUG("Result stdout: '%s' stderr: '%s'", NULLSTR(*cmd->outbuf), NULLSTR(*cmd->errbuf)); as cmd->outbuf and cmd->errbuf are NULL. The two if blocks before that setup cmd->outbuf and cmd->errbuf in case the caller didn't request output capturing aren't executed because the caller requested to capture the output to FDs. /* If caller hasn't requested capture of stdout/err, then capture * it ourselves so we can log it. */ if (!cmd->outfdptr) { cmd->outfdptr = &cmd->outfd; cmd->outbuf = &outbuf; } if (!cmd->errfdptr) { cmd->errfdptr = &cmd->errfd; cmd->errbuf = &errbuf; } In the case the caller requested to capture the output to FDs there is no capturing to cmd->outbuf and cmd->errbuf and they stay NULL. When I remove that offending VIR_DEBUG line everything works fine. Also this case of FD only usage is not yet covered in the command API test cases. Matthias