The launchctl binary file is located in /bin.
If you type "launchctl help", you get a list of available commands. This is the output of "launchctl help" when done on an iPod Touch 2nd Generation running iOS 4.2.1:
usage: launchctl <subcommand> load Load configuration files and/or directories unload Unload configuration files and/or directories start Start specified job stop Stop specified job submit Submit a job from the command line remove Remove specified job bootstrap Bootstrap launchd list List jobs and information about jobs setenv Set an environmental variable in launchd unsetenv Unset an environmental variable in launchd getenv Get an environmental variable from launchd export Export shell settings from launchd debug Set the WaitForDebugger flag for the target job to true. limit View and adjust launchd resource limits stdout Redirect launchd's standard out to the given path stderr Redirect launchd's standard error to the given path shutdown Prepare for system shutdown singleuser Switch to single-user mode getrusage Get resource usage statistics from launchd log Adjust the logging level or mask of launchd umask Change launchd's umask bsexec Execute a process within a different Mach bootstrap subset bslist List Mach bootstrap services and optional servers bstree Show the entire Mach bootstrap tree. Requires root privileges. managerpid Print the PID of the launchd managing this Mach bootstrap. manageruid Print the UID of the launchd managing this Mach bootstrap. managername Print the name of this Mach bootstrap. exit Exit the interactive invocation of launchctl quit Quit the interactive invocation of launchctl help This help output
This command does not need to be run as root. Mobile will do fine. Also, this command should not differ much on your device from that of my test-device. If it does, please let me know and I will update this page accordingly.
Before iOS 6.1.3, this command used the arguements located in /etc/launchd.conf and executed them on startup. This is how evasi0n achieved an untethered jailbreak. Please see launchd.conf untether for more information.