Can not start MongoDB 3.2.1 on CentOS 7 -

i followed doc install mongodb 3.2.1 on centos 7. after installing, change owner , group of var/lib/mongo , var/log/mongodb/mongod.log root:root.

when start mongodb service mongod start, shows

starting mongod (via systemctl):  job mongod.service failed. see 'systemctl status mongod.service' , 'journalctl -xn' details.[failed] 

i have run 2 commands show details.

systemctl status mongod.service shows

mongod.service - sysv: mongo scalable, document-oriented database.    loaded: loaded (/etc/rc.d/init.d/mongod)    active: failed (result: exit-code) since wen 2016-01-27 18:32:46 cst; 14s ago   process: 24913 execstart=/etc/rc.d/init.d/mongod start (code=exited, status=1/failure)  main pid: 23711 (code=exited, status=0/success)  1月 27 18:32:45 server1 systemd[1]: starting sysv: mongo scalable, document-oriented database.... 1月 27 18:32:45 server1 runuser[24920]: pam_unix(runuser:session): session opened user mongod (uid=0) 1月 27 18:32:46 server1 mongod[24913]: starting mongod: [failed] 1月 27 18:32:46 server1 systemd[1]: mongod.service: control process exited, code=exited status=1 1月 27 18:32:46 server1 systemd[1]: failed start sysv: mongo scalable, document-oriented database.. 1月 27 18:32:46 server1 systemd[1]: unit mongod.service entered failed state. 

journalctl -xn shows

-- logs begin @ 日 2016-01-24 16:33:05 cst, end @ wen 2016-01-27 18:32:46 cst. -- 1月 27 18:32:15 server1 sshd[24879]: pam_succeed_if(sshd:auth): requirement "uid >= 1000" not met user "root" 1月 27 18:32:17 server1 sshd[24879]: failed password root 182.100.67.59 port 10013 ssh2 1月 27 18:32:45 server1 sudo[24896]: root : tty=pts/0 ; pwd=/var/log/mongodb ; user=root ; command=/sbin/service mongod start 1月 27 18:32:45 server1 systemd[1]: starting sysv: mongo scalable, document-oriented database.... -- subject: unit mongod.service has begun start-up -- defined-by: systemd -- support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel --  -- unit mongod.service has begun starting up. 1月 27 18:32:45 server1 runuser[24920]: pam_unix(runuser:session): session opened user mongod (uid=0) 1月 27 18:32:46 server1 runuser[24920]: pam_unix(runuser:session): session closed user mongod 1月 27 18:32:46 server1 mongod[24913]: starting mongod: [failed] 1月 27 18:32:46 server1 systemd[1]: mongod.service: control process exited, code=exited status=1 1月 27 18:32:46 server1 systemd[1]: failed start sysv: mongo scalable, document-oriented database.. -- subject: unit mongod.service has failed -- defined-by: systemd -- support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel --  -- unit mongod.service has failed. --  -- result failed. 1月 27 18:32:46 server1 systemd[1]: unit mongod.service entered failed state. 

i accessed server ssh key, no password.

is reason change ownership root?

both /var/lib/mongo , /var/log/mongodb should writable mongodb user.

by default mongodb:mongodb. check user runs mongodb service in /etc/init.d/mongodb. if daemonuser=${daemonuser:-mongodb} chown directories user.