This article discusses the following syslog message:

CHASSISD_EXEC_ERROR: srx550_set_fan_speed fd is -1: Bad file descriptor

Sometimes, the following syslog message is generated when the commit command is issued on an SRX550.

This issue only occurs when executing a commit to start a child chassisd on an SRX550.  However, this process is quickly cleaned up when the config commit process completes.
This message does not affect performance and can be safely ignored.