Some notes on the EX300 exam.

• Source: https://www.redhat.com/en/services/training/ex300-red-hat-certified-engineer-rhce-exam

• Start with two systems, having at least two networkinterfaces.
• Bonding is not supported with cross cables, or direct links. If an interface is administratively disabled in such a configuration, the PHY may still maintain electrical connectivity to the peer and failover will not work as expected, leading to a lack of bond communication.

Teaming is new in RHEL 7.

• First, install the team daemon, if it has not been installed yet:

  yum install teamd

• Create a new team interface:

  nmcli connection add type team con-name team0

• Add interfaces to the team:

  nmcli con add type team-slave ifname enp2s0 master team0
  nmcli con add type team-slave ifname enp3s0 master team0

• Bring interfaces up (first the ports, then master):

  nmcli c up team-slave-enp2s0
  nmcli c up team-slave-enp3s0
  nmcli c up team0

• Team status:

  teamdctl nm-team state
  setup:
    runner: roundrobin
  ports:
    enp3s0
      link watches:
        link summary: up
        instance[link_watch_0]:
          name: ethtool
          link: up
          down count: 0
    enp2s0
      link watches:
        link summary: up
        instance[link_watch_0]:
          name: ethtool
          link: up
          down count: 0

• Team port status:

  teamnl nm-team ports
   4: enp3s0: up 1000Mbit FD 
   3: enp2s0: up 1000Mbit FD

• Modify the runner type:

  nmcli con mod team0 team.config '{ "runner": {"name": "loadbalance"}}'

Runners

• broadcast (data is transmitted over all ports)
• round-robin (data is transmitted over all ports in turn)
• active-backup (one port or link is used while others are kept as a backup)
• loadbalance (with active Tx load balancing and BPF-based Tx port selectors)
• lacp (implements the 802.3ad Link Aggregation Control Protocol)

In addition, the following link-watchers are available:

• ethtool (Libteam lib uses ethtool to watch for link state changes). This is the default if no other link-watcher is specified in the configuration file.
• arp_ping (The arp_ping utility is used to monitor the presence of a far-end hardware address using ARP packets.)
• nsna_ping (Neighbor Advertisements and Neighbor Solicitation from the IPv6 Neighbor Discovery protocol are used to monitor the presence of a neighbor's interface)

There are no restrictions in the code to prevent a particular link-watcher from being used with a particular runner, however when using the lacp runner, ethtool is the only recommended link-watcher.

• Create a bond:

  nmcli con add type bond con-name bond0 ifname bond0 mode active-backup

• Add slaves:

  nmcli con add type bond-slave ifname enp2s0 master bond0

• Bring up slaves and then the bond0 interface:

  nmcli con up bond-slave-enp2s0
  nmcli con up bond-slave-enp3s0
  nmcli con up bond0

• Change bond options:

  nmcli con mod bond0 +bond.options mii=100
  nmcli con mod bond0 +bond.options mode=802.3ad

• Show bond statistics:

  cat /proc/net/bonding/bond0 
  Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)
  
  Bonding Mode: load balancing (round-robin)
  MII Status: up
  MII Polling Interval (ms): 100
  Up Delay (ms): 0
  Down Delay (ms): 0
  
  Slave Interface: enp2s0
  MII Status: up
  Speed: 1000 Mbps
  Duplex: full
  Link Failure Count: 1
  Permanent HW addr: 00:0d:b9:33:90:75
  Slave queue ID: 0
  
  Slave Interface: enp3s0
  MII Status: up
  Speed: 1000 Mbps
  Duplex: full
  Link Failure Count: 1
  Permanent HW addr: 00:0d:b9:33:90:76
  Slave queue ID: 0
  

• Add static IPv6 address:

  nmcli c edit enp1s0
  nmcli> set ipv6.addresses 2001:470:xxxx:xxxx::10/64
  nmcli> set ipv6.gateway 2001:470:xxxx:xxxx::1
  nmcli> save
  nmcli> quit
  nmcli c up enp1s0

• Troubleshoot with:
  • Ping: ping6
  • Traceroute: traceroute6
  • Resolve hostnames: host -t AAAA <ipv6 hostname>
  • Show routes: ip -6 r
  • Show neighbours: ip neigh
  • Portscan: nmap -6 <ipv6 address>
  • Show firewall rules: ip6tables -nvL
  • Telnet test, Star Wars: telnet towel.blinkenlights.nl
  • Telnet test, BOFH excuse server: telnet towel.blinkenlights.nl 666

• Show routes: ip -r
• Add static route: nmcli edit connection → set ipv4.routes 1.2.3.4/24 1.2.3.1
• Remove static route: nmcli edit connection → remove ipv4.routes 1.2.3.4/24 1.2.3.1
• NMcli saves config in /etc/sysconfig/network-scripts. You can also disable NetworkManager and create the config yourself.

• List current active zones: firewall-cmd --get-active-zones
• List default zone: firewall-cmd --get-default-zone
• List all information in zone: firewall-cmd --zone public --list-all
• To Make rules permanent, use: --permanent
• Reload after using --permanent: firewall-cmd --reload

• Open port: firewall-cmd --permanent --zone internal --add-service ssh
• Instead of opening a port/service, remove a service with: --remove-service

• Add a source to zone: firewall-cmd --permanent --zone internal --add-source 1.2.3.4/24
• Instead of adding a source, remove it with: --remove-source

• Add new service XML files to /etc/firewalld/services/, find examples in: /usr/lib/firewalld/services/.

• Add masquerading: firewall-cmd --permanent --zone=external --add-masquerade
• Port forwarding (check if forwarding is enabled in kernel): firewall-cmd --permanent --zone=external --add-forward-port=port=22:proto=tcp:toport=2222

• Direct rule example:firewall-cmd --permanent --direct --add-rule ipv4 filter INPUT 0 -p tcp --dport 5001 -j ACCEPT
• List all direct rules: firewall-cmd --direct --get-all-rules

• Change variable temporary: echo 1 >/proc/sys/net/ipv4/ip_forward
• Make it permanent, edit /etc/sysctl.d/<name>.conf. And run sysctl -p
• Read all variables with sysctl: sysctl -a

• Install the required packages:

  yum -y install krb5-workstation pam_krb5

• Edit the /etc/krb5.conf file:
  • Uncomment all lines.
  • Replace al example domain names and realms.
  • Change example kdc and admin_server.
• Add principals on KDC:

  kadmin -p root/admin
  kadmin:  addprinc -randkey host/test1.example.com
  kadmin:  addprinc -randkey host/test2.example.com
  kadmin:  addprinc -randkey host/test3.example.com
  
  kadmin:  ktadd host/test1.example.com
  kadmin:  ktadd host/test2.example.com
  kadmin:  ktadd host/test3.example.com

• Retrieve ticket:

  kinit benst

Initiator

• Configure system as client (initiator), install the required packages:

   yum install iscsi-initiator-utils

• Edit /etc/iscsi/initiatorname.iscsi and set the InitiatorName. For example:

  InitiatorName=iqn.2016-04.nl.polaire:test4

• Edit /etc/iscsi/iscsid.conf and change username an password:

  node.session.auth.authmethod = CHAP
  node.session.auth.username = <username>
  node.session.auth.password = <password>

• Start the iSCSI service:

  systemctl start iscsi

• Discover targets:

  iscsiadm --mode discovery --type sendtargets --portal 1.2.3.4

• Log in on target:

  iscsiadm --mode node --targetname iqn.2000-01.nl.polaire:rackstation.target-Test --portal 1.2.3.4 --login

• You have now access to the block device:

  lsblk --scsi
  NAME HCTL       TYPE VENDOR   MODEL             REV TRAN
  sda  1:0:0:0    disk ATA      KINGSTON SMS200S BBF0 sata
  sdc  7:0:0:0    disk SYNOLOGY IBLOCK           4.0  iscsi

• You can now create a file system (or use LVM first) and mount it at boot.
  • Create file system and mount at boot:

    mkfs.xfs /dev/sdc
    mkdir /data
    mount /dev/sdc /data
    echo "UUID=`blkid -s UUID -o value /dev/sdc` /data xfs _netdev 0 0" >>/etc/fstab
    
    umount /data
    mount -a
    
    # test reboot

• Show nodes:

  iscsiadm -m discoverydb -P1

• If you need to delete a node:

  iscsiadm -m node -p 172.16.10.39 --op=delete

• If you have the problem that systemd unmounts a new volume after altering /etc/fstab, run systemctl daemon-reload.

Target

• Install targetcli:

  yum install -y targetcli</code.
    * Enable service (start at boot):<code>systemctl enable target

• Create file backed store:

  targetcli
  /> backstores/fileio/ create shareddata /opt/iscsi.img 1G
  Created fileio shareddata with size 1073741824
  /> iscsi/ create iqn.2016-04.nl.polaire:target1
  Created target iqn.2016-04.nl.polaire:target1.
  Created TPG 1.
  Global pref auto_add_default_portal=true
  Created default portal listening on all IPs (0.0.0.0), port 3260.

• You can cd into that directory and create a portal if it has not been created yet:

  targetcli
  /> cd iscsi/iqn.2014-08.com.example:t1/tpg1
  /> portals/ create

• Create a LUN:

  targetcli
  /iscsi/iqn.20...laire:target1> luns/ create /backstores/fileio/shareddata

• Create ACL:

  acls/ create iqn.2016-04.nl.polaire:test4

• Set password:

  /iscsi/iqn.20...ample:t1/tpg1> cd acls/iqn.2016-04.nl.polaire:test4/
  /iscsi/iqn.20...xample:client> set auth userid=username
  Parameter userid is now 'username'.
  /iscsi/iqn.20...xample:client> set auth password=pwd

• Config is saved in /etc/target/saveconfig.json

• Open firewall port:

  firewall-cmd --permanent --add-port=3260/tcp
  firewall-cmd --reload

• top, sar, vmstat, iostat, tcpdump…

• bash scripting…

• yum, rpm

• ls -lZ
• restorecon
• semanage
• auditd

• Install tools:

  yum install policycoreutils-python

• List ports:

  semanage port -l | grep ssh

• Modify port setting:

  semanage port -m -t ssh_port_t -p tcp 4321

• Enable server to start at boot:

  systemctl enable <servicename>

• systemctl start
  systemctl stop
  systemctl restart
  systemctl enable
  systemctl reeanble
  systemctl status

• Add custom services in: /etc/systemd/system.

• ?

HTTP/HTTPS

• Install httpd:

  yum install httpd

• Enable service:

  systemctl enable httpd

• Create a directory for the virtual host files:

  mkdir /var/www/html/virta

• Create a index.html:

  echo "
  <html>
  <head><title>virta virtual host</title></head>
  <body>
  This is virtual host -virta-
  </body>
  </html>
  " > /var/www/html/virta/index.html

• Restore SELinux labels if needed:

  restorecon -Rv /var/www/html/

• Create the virtual host config in, config is read alphabetically/etc/httpd/conf.d/1-virta.conf. You can find examples in /usr/share/doc/httpd-2.4.6/httpd-vhosts.conf:

  <VirtualHost *:80>
      ServerAdmin ben@polaire.nl
      DocumentRoot "/var/www/html/virta/"
      ServerName virta.polaire.nl
      ServerAlias www.virta.polaire.nl
      ErrorLog "/var/log/httpd/virta-error_log"
      CustomLog "/var/log/httpd/virta-access_log" common
  </VirtualHost>

• You van add the virta hostname in DNS, or for this test in the /etc/hosts file.
• Test config:

  apachectl configtest

• Start httpd:

  systemctl start httpd

• Open firewall port:

  firewall-cmd --permanent --zone public --add-service http
  firewall-cmd --reload

• Show all running virtual hosts:

  httpd -D DUMP_VHOSTS

• Test with elinks on local host.

• Create a private directory:

  mkdir /var/www/html/virta/private

• Create a test file:

  echo "This is private" >/var/www/html/virta/private/index.html

• Add the config below for host based authentication:

  <Directory "/var/www/html/virta/private">
  AllowOverride None
  Options None
  Require host test.polaire.nl localhost
  </Directory>

• For user based authentication, create the following config:

  <Directory "/var/www/html/virta/private/">
  AuthType Basic
  AuthName "Password protected"
  AuthUserFile /etc/httpd/conf/passwd
  Require user testuser
  </Directory>

• Save the user and password:

  htpasswd -c /etc/httpd/conf/passwd testuser

• Modify rights:

  chmod 600 /etc/httpd/conf/passwd
  chown apache:apache /etc/httpd/conf/passwd

• Simple method is to put an executable perl script in: /var/www/cgi-bin.
• Or create a bash script and configure the vhost:

  <Directory "/usr/local/cgi-bin/">
      Options +ExecCGI
      AddHandler cgi-script .cgi
    </Directory>

• Bash script:

  #!/bin/bash
  echo "Content-type: text/html"
  date
  echo
  echo "Testing CGI scripts..."

• Configure the directory directive:

  AuthType Basic
  AuthName "Group test"
  AuthGroupFile /etc/httpd/conf/group
  AuthUserFile /etc/httpd/conf/passwd
  Require group usergroup

• Create the group file /etc/httpd/conf/group:

  usergroup: user1 user2

• Create the password file /etc/httpd/conf/passwd:

  htpasswd -c /etc/httpd/conf/passwd user1
  htpasswd /etc/httpd/conf/passwd user2

• Have the httpd server running.
• Install the required packages (haveged for speeding up key generation):

  yum install crypto-utils mod_ssl lynx haveged

• Start and enable haveged:

  systemctl start haveged
  systemctl enable haveged

• Run genkey (use --test to omit the slow process of generating random data) :

  genkey server.domain.tld

• Edit: /etc/httpd/conf.d/ssl.conf:

  SSLCertificateFile /etc/pki/tls/certs/test.polaire.nl.crt
  SSLCertificateKeyFile /etc/pki/tls/private/test.polaire.nl.key
  ServerName test.polaire.nl:443

• Create a new virtual host for HTTPS, see example in ssl.conf.
• Check config and restart Apache:

  apachectl configtest
  systemctl restart httpd:

• Open firewall https port 443.
• Test with lynx

DNS

• Install unbound:

  yum install unbound

• Configure unbound, edit /etc/unbound/unbound.conf:

          interface: 0.0.0.0
          interface: ::0
  
          do-ip4: yes
          do-ip6: yes
  
          do-udp: yes
  
          use-syslog: yes
          
          hide-identity: yes
          hide-version: yes
   
          #val-permissive-mode: yes # Might be needed if upstream doesn't support DNSSEC
  
          access-control: 0.0.0.0/0 allow
          access-control: ::0/0 allow
          
          domain-insecure: "your-domain.tld"
  

• Create a forward zone (for all zones) /etc/unbound/conf.d/forward.conf:

  forward-zone:
          name: "."
          forward-addr: 1.2.3.4
          forward-addr: 1.2.3.5

• Check config: unbound-checkconf /etc/unbound/unbound.conf.
• Enable and start the service:

  systemctl start unbound.service
  systemctl enable unbound.service

• Open firewall ports (53 udp).

• Use the host or dig command. Check journalctl.

NFS

• Install packages:

  yum groupinstall file-server

• Open firewall:

  firewall-cmd --permanent --add-service=nfs
  firewall-cmd --reload

• Start services and configure to start at boot:

  systemctl enable rpcbind nfs-server
  systemctl start rpcbind nfs-server

• Create shared directory:

  mkdir -p /home/share1
  chmod 0777 /home/share1
  mkdir -p /home/share2
  chmod 0777 /home/share2

• Set SELinux contexts:

  semanage fcontext -a -t public_content_rw_t "/home/share1(/.*)?"
  semanage fcontext -a -t public_content_rw_t "/home/share2(/.*)?"
  restorecon -Rv /home/share1
  restorecon -Rv /home/share2

• Create shares, edit /etc/exports:

  /home/share1 test1.yourdomain.tld(rw,no_root_squash)
  /home/share2 test2.yourdomain.tld(rw,no_root_squash)

• Export the filesystems:

  exportfs -avr
  # systemctl restart nfs-server

• For showmount to work, open firewall for additional ports:

  firewall-cmd --add-service=mountd --permanent
  firewall-cmd --add-service=rpc-bind --permanent
  firewall-cmd --reload

• Configure the client:

  yum install nfs-utils
  showmount -e nfs.yourdomain.tld
  mount -t nfs nfs.yourdomain.tld:/home/share1 /mnt

• Create an NFS server.
• Create a shared directory.
• Create a group.
• Assign group to shared directory.
• Set permissions to directory.

  chmod 0770 /home/Shared # no sticky or setgid bit.
  All group users can add to and delete from the folder and can read and but not write to each others files.
  
  chmod 1770 /home/Shared # sticky bit
  Same as above but only the owner of the file can delete it.
  
  chmod 2770 /home/Shared # setgid bit
  All group users can add to and delete from the folder and can read and write to each other's files:
  
  chmod 3770 /home/Shared # sticky and setgid bit
  As above, except only the owner of the file can delete it

• Create /etc/exports.

  /shared client(rw,no_root_squash)

• Export the directory:

  exportfs -avr
  systemctl restart nfs-server

• Configure working NTP (NTPd or Chrony) and DNS.
• Install Kerberos KDC:

  yum install krb5-server krb5-workstation pam_krb5
  yum install haveged (for entropy)
  systemctl start haveged
  systemctl enable haveged
  
  vi /var/kerberos/krb5kdc/kdc.conf  # replace EXAMPLE.COM with your own realm
                                     # uncomment master_key_type = aes256-cts line
                                     # and paste the following line in the [realms] stanza:
                                     # default_principal_flags = +preauth
  
  vi /etc/krb5.conf                  # uncomment all the lines, replace EXAMPLE.COM with your own realm
                                     # example.com with your own domain name, and kerberos.example.com
                                     # with your own KDC server name (here kbserver.example.com).
  
  vi /var/kerberos/krb5kdc/kadm5.acl # replace EXAMPLE.COM with your own realm.
  
  
  # Create Kerberos database
  kdb5_util create -s -r YOURDOMAIN.TLD
  
  # Start and activate Kerberos
  systemctl start krb5kdc kadmin
  systemctl enable krb5kdc kadmin
  
  # Add users
  useradd test1
  useradd test2
  
  # Start Kerberos admin
  kadmin.local
  
  # Create admin principal
  kadmin.local:   addprinc root/admin
  
  # Create user principals
  kadmin.local:   addprinc test1
  kadmin.local:   addprinc test2
  
  # Add KDC hostname
  kadmin.local:   addprinc -randkey host/kbserver.yourdomain.tld
  
  # Create local copy /etc/krb5.keytab file:
  kadmin.local:  ktadd host/kbserver.yourdomain.tld
  
  kadmin.local:  quit
  
  
  # Open firewall
  firewall-cmd --permanent --zone public --add-service kerberos
  firewall-cmd --reload
  
  # Test
  su - test1
  kinit
  klist

• Setup an NFS server:

  yum groupinstall file-server
  firewall-cmd --permanent --add-service=nfs
  firewall-cmd --permanent --add-service=mountd 
  firewall-cmd --permanent --add-service=rpc-bind
  firewall-cmd --reload
  
  # Activate and start NFS server
  systemctl enable rpcbind nfs-server
  systemctl start rpcbind nfs-server
  
  # Create a shared directory
  mkdir -p /home/share
  chmod 0777 /home/share
  yum install policycoreutils-python # provides the semanage command
  semanage fcontext -a -t public_content_rw_t "/home/share(/.*)?"
  restorecon -Rv /home/share
  echo "/home/share client.example.com(rw,no_root_squash)" >> /etc/exports
  exportfs -avr
  showmount -e localhost

• Configure the NFS client:

  yum install nfs-utils
  showmount -e nfsserver.yourdomain.tld
  mount -t nfs nfsserver.yourdomain.tld:/home/share /mnt

• Configure the NFS server and NFS client as kerberos client.

  # Install on both NFS server and client:
  yum install krb5-workstation pam_krb5
  
  # Copy the /etc/krb5.conf file from the KDC server to NFS client and server.
  
  # Add the principals (on the KDC)
  kadmin
  kadmin:  addprinc -randkey nfs/nfserver.yourdomain.tld
  kadmin:  addprinc -randkey nfs/nfsclient.yourdomain.tld
  kadmin:  ktadd nfs/nfsserver.yourdomain.tld
  kadmin:  ktadd nfs/nfsclient.yourdomain.tld
  kadmin:  quit
  
  # Add sec=krb5 to exports on NFS server
  /home/share nfsclient.yourdomain.tld(rw,no_root_squash,sec=krb5)
  
  # Activate and start NFS on the server (RHEL 7.0 only)
  systemctl enable nfs-secure-server && systemctl start nfs-secure-server
  
  # Copy /etc/krb5.keytab from KDC to client.
  
  # Activate and start NFS on the client: 
  # RHEL 7.0
  # systemctl enable nfs-secure && systemctl start nfs-secure
  
  # RHEL >= 7.1
  # systemctl enable nfs-client.target && systemctl start nfs-client.target
  
  # Mount the remote directory:
  mount -t nfs4 -o sec=krb5 nfsserver.yourdomain.tld:/home/tools /mnt

SMB

• Install packages:

  yum groupinstall "File and Print Server"

• Create directory:

  mkdir /opt/smbdata

• Set rights:

  chown testuser.users /opt/smbdata
  chmod 775 /opt/smbdata

• Set SELinux context:

  semanage fcontext -a -t samba_share_t "/opt/smbdata(/.*)?"
  restorecon -Rv /opt/smbdata

• Edit /etc/samba/smb.conf
  • Change workgroup.
  • Add share:

    [data]
            comment = Data
            path = /opt/smbdata
            browseable = yes
            writeable = yes
            hosts allow = 10.1.2.
            valid users = testuser

• Test config with: testparm.
• Enable and start smb, nmb and winbind.
• Create user:

  useradd -s /sbin/nologin testuser
  smbpasswd -a testuser

• Open firewall for CIFS (samba) traffic.
• Test:

  smbclient //localhost/shared -U testuser

• On the client install the required packages:

  yum install cifs-utils samba-client

• Test connection:

  smbclient -L <server> -U <username>
  smbclient //server/data -U <username>

• Without using Kerberos, you could use a multiuser mount. You can then use cifscreds to login to a multiuser mount.
• Create a credentials file /root/smb-creds:

  username=user01
  password=...

• Test with:

  mount -t cifs -o multiuser,credentials=/root/smb-creds //test6/data /mnt

• Switch to other user and use cifscreds
• Test if you can r/w files.
• Mount in fstab:

  //test6/data /mnt cifs multiuser,credentials=/root/smb-creds 0 0

SMTP

• Edit /etc/postfix/main.cf, restart postfix.
• check options man 5 postconf.

SSH

NTP