You may come across a case, when you access Webmin, only system information is displayed and there are no options on the left pane. Only logout.
In that case, check the file mentioned below for webmin user.
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/etc/webmin/webmin.acl
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Add the webmin admin user with the following services
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webmin_admin_2gmw: acl adsl-client ajaxterm apache at backup-config bacula-backup bandwidth bind8 burner cfengine change-user cluster-copy cluster-cron cluster-passwd cluster-shell cluster-software cluster-useradmin cluster-usermin cluster-webmin cpan cron custom dfsadmin dhcpd dnsadmin dovecot exim exports fdisk fetchmail file filter firewall frox fsdump grub heartbeat htaccess-htpasswd idmapd inetd init inittab ipfilter ipfw ipsec iscsi-client iscsi-server iscsi-target jabber krb5 ldap-client ldap-server ldap-useradmin lilo logrotate lpadmin lvm mailboxes mailcap majordomo man mon mount mysql net nis openslp package-updates pam pap passwd phpini postfix postgresql ppp-client pptp-client pptp-server proc procmail proftpd pserver qmailadmin quota raid samba sarg sendmail sentry servers shell shorewall shorewall6 smart-status smf software spam squid sshd status stunnel syslog-ng syslog system-status tcpwrappers telnet time tunnel updown useradmin usermin vgetty webalizer webmin webmincron webminlog wuftpd xinetd
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Now restart webin and reload the page. You should have all the options on the left pane.