$ netmiko-cfg --cmd 'set system syslog log-rotate-frequency 5' juniper
configure
Entering configuration mode
Users currently editing the configuration:
root terminal u0 (pid 23534) on since 2016-12-28 20:59:23 EST, idle 6w6d 05:42
[edit]
The configuration has been changed but not committed
[edit]
pyclass@pynet-jnpr-srx1# set system syslog log-rotate-frequency 5
[edit]
pyclass@pynet-jnpr-srx1# exit configuration-mode
The configuration has been changed but not committed
Exiting configuration mode
pyclass@pynet-jnpr-srx1>
(py27_netmiko)[gituser@ip-10-178-21-224 ~]$ netmiko-cfg --cmd 'set system syslog log-rotate-frequency 5\ncommit' juniper
Second command just hangs indefinitely.