centos7系统root无法通过su切换到某个普通用户

[root@namenode01 backup]# su - app
Last login: Tue Apr 26 09:48:44 CST 2016 from application03 on pts/0
su: failed to execute /bin/bash: Resource temporarily unavailable

[root@namenode01 backup]# egrep -v "^$|^#" /etc/security/limits.d/20-nproc.conf
*          soft    nproc     65535        #将默认值1024改为65535
root       soft    nproc     unlimited

[root@namenode01 backup]# su - app
Last login: Tue Apr 26 10:38:20 CST 2016 on pts/0
[app@namenode01 ~]$ id
uid=1001(app) gid=1001(app) groups=1001(app) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023