RHCE 7 Summary

Repositories and Host Allowance/Denial

man 5 hosts_access

# vim /etc/yum.repos.d/rhce.repo

[RHCE_RHEL7]
name=RHCE_RHEL7
baseurl=http://<baseurl>
enabled=1
gpgcheck=0

The following command will do it automatically:

sudo yum-config-manager --add-repo http://server.example.com/rep

cat /etc/yum.repos.d/server.example.com_repo.rep

[server.example.com_repo]
name=added from: http://server.example.com/repo
baseurl=http://server.example.com/repo
enabled=1

# yum repolist

yum Commands

Show Installed Packages

# yum list installed

Download Package

# yumdownloader <package>

Check for Updates

# yum check-update

Shows Package Info

# yum info <package>

1. Allow SSH for a domain and deny SSH to all the others

# vim /etc/hosts.allow

sshd: .domain.com

# vim /etc/hosts.deny

sshd: ALL

2. Allow SSH for specific IP and block all the others

# vim /etc/hosts.deny

sshd: ALL EXCEPT 192.168.0.1

3. Denies all services to all hosts unless permitted in hosts.allow

# vim /etc/hosts.allow

ALL: .foobar.edu EXCEPT terminalserver.foobar.edu

# vim /etc/hosts.deny

ALL

4. Access granted by default, redundant file hosts.allow

# vim /etc/hosts.deny

some.host.name, .some.domain

# vim /etc/hosts.deny

ALL EXCEPT in.fingerd: other.host.name, .other.domain

5. Rules can be also in one file, for example

# vim /etc/hosts.allow

ALL: .friendly.domain: ALLOW
ALL: ALL: DENY

# vim /etc/hosts.allow

ALL: .bad.domain: DENY
ALL: ALL: ALLOW

Recover root password

reboot
e
linux16...
rd.break enforcing=0
ctrl+x
switch_root:/# mount –oremount,rw /sysroot
switch_root:/# chroot /sysroot
sh-4.2# passwd root
Changing password for user root.
New passwd: mypassword
Retype new password: mypassword
passwd: all authentication token updated successfully.
sh-4.2# exit
switch_root:/# exit
logout

...
[  OK  ] Started Network Manager Script Dispatcher Service.
[  OK  ] Started Crash recovery kernel arming.
[  OK  ] Reached target Multi-User System.

CentOS Linux 7 (Core)
Kernel 3.10.0-229.14.1.el7.x86_64 on an x86_64

vm login: root
Password: mypassword

# restorecon /etc/shadow
# setenforce enforcing

## Configure Key-Based Authentication

yum install openssl
ssh-keygen -b 2048 -t rsa
ssh-copy-id -i .ssh/id_rsa.pub [email protected]

Edit the /etc/ssh/sshd_config

PasswordAuthentication no
PubkeyAuthentication yes

Temporarily Store passphrase

ssh-agent bash
ssh-add
Enter passphrase for /user/.ssh/id_rsa:

systemctl restart sshd

SERVICES

systemctl --failed --type=service
systemctl show <unit>
systemctl status <-l> <unit> <-l>
systemctl stop|start|restart|reload <unit>
systemctl mask|unmask <unit>
systemctl enable|disable <unit>
systemctl list-dependencies <unit>
systemctl list-units --type=service --all
systemctl list-unit-files --type=service
systemctl get-default
systemctl set-default <graphical|multi-user|rescue|emergency>
systemctl isolate <graphical|multi-user|rescue|emergency>

IPV4

nmcli dev status
nmcli con show <name>
nmcli con show --active
ip addr show <eth0> / ip a
ip link / ip l
nmcli con add con-name <name> type ethernet ifname <eth0> ip4 xxx.xxx.xxx.xxx/24 gw4 xxx.xxx.xxx.xxx
nmcli con mod <name> ipv4.addresses "192.0.2.2/24 192.0.2.254"
nmcli con <up|down> <name>
nmcli dev status
nmcli dev dis <eth0>
nmcli con mod <name> +ipv4.dns xxx.xxx.xxx.xxx
    vim /etc/sysconfig/network-script/ifcfg-<name>
nmcli con reload
nmcli con del <name>
hostname
hostnamectl set-hostname <name>
    vim /etc/hostname
hostnamectl status
ip route / ip r
ss -tulpn | grep sshd

Add Route

man (8) ip-route

ip route add 213.97.191.187/32 via 192.168.1.1 dev eth1

Static Route

vim /etc/sysconfig/static-routes

any net 172.194.229.0 netmask 255.255.255.0 gw 192.168.1.1 dev eth1

IPV6

nmcli con add con-name <name> type ethernet ifname <eth0> ip6 xxxx:xxxx:xxx:x:x:x/64 gw6 xxxx:xxxx:xxx:x:x:x
ip -6 route show
ping6 xxxx:xxxx:xxx:x:x:x
ping6 xxxx:xxxx:xxx:x:x:x<%eth1> for link-local addresses and multicast groups
tracepath6 xxxx:xxxx:xxx:x:x:x
ss -A inet -n
netstat -46n
nmcli con mod <name> ipv6.method manual

TEAMING

man 5 nmcli-examples man 5 teamd.conf /usr/share/doc/teamd-1.25

nmcli con add con-name <team0> type team ifname <team0> config '{ "runner": { "name": "<activebackup|broadcast|loadbalance|roundrobin|lacp>"}}'

Must be before ipv4.method

nmcli con mod <team0> ipv4.address xxx.xxx.xx.x/24

nmcli con mod <team0> ipv4.method manual
nmcli con mod <team0> connection.autoconnect yes

or autoconect yes during con add

nmcli con add con-name <team0-port1> type team-slave ifname <eth0> master <team0>
nmcli con add con-name <team0-port2> type team-slave ifname <eth1> master <team0>

-con-name <teamX-portX> not necessary, default is team-slave-<IFACE>

nmcli con up <team0>
nmcli con up team0-port1
nmcli con up team0-port2
nmcli dev dis eth1
teamdctl <team0> state
teamdctl <team0> config dump
teamnl <team0> ports
teamnl <team0> options
teamnl <team0> getoption activeport
teamnl <team0> setoption activeport <2>

If you make a mistake:

nmcli con mod <team0> team.config ‘{“runner”:{“name”:”activebackup”}}’

BRIDGING

nmcli con add con-name <bridge0> type bridge ifname <br0>
b/ nmcli con add con-name <bridge0-port1> type bridge-slave ifname <eth0> master <br0>
c/ nmcli con add con-name <bridge0-port2> type bridge-slave ifname <eth1> master <br0>
brctl show

BRIDGE=brteam0 /etc/sysconfig/network-scripts/ifcfg-team

FIREWALL

man 5 firewalld.richlanguage

Understand Zones

man firewalld.zones

systemctl mask <iptables|ip6tables|ebtables>
firewall-cmd --set-default zone=<dmz|trusted|home|internal|work|public|external|block|drop>

trusted=all incoming traffic allowed
home=reject incoming unless matching outgoing, accept incoming ssh,mdns,ipp-client,samba-client,dhcpv6-client
internal=same as home
work=reject incoming unless matching outgoing, accept incoming ssh,ipp-client,dhcpv6-client
public=reject incoming unless matching outgoing, accept incoming ssh,dhcpv6-client [DEFAULT]
external=reject incoming unless matching outgoing, accept incoming ssh, masquerading enabled
dmz=reject incoming unless matching outgoing, accept incoming ssh
block=reject incoming unless matching outgoing
drop=reject incoming unless matching outgoing, does not respond at all

Rules

/etc/firewall.d; /usr/lib/firewalld

firewall-cmd --<get-default-zone|set-default-zone|get-zones|get-services|get-active-zones|list-all>
firewall-cmd --<add|remove-rich-rule=RULE|query-rich-rule=RULE|list-rich-rules>
firewall-cmd --<remove-service=SERVICE|remove-port=PORT/PROTOCOL>
firewall-cmd --permanent --zone=<name> --add-source=xxx.xxx.xx.x/24
firewall-cmd --timeout=60 --zone=<name> --add-service=mysql
firewall-cmd --reload
firewall-cmd --remove-service=haproxy –zone=public
firewall-cmd --direct --get-all-rules
firewall-cmd --get-zone-of-interface=eth0

## Rich Rules

rule source destination [service|port|masquerade|forward-port] log audit

firewall-cmd --permanent --zone=<name> --add-rich-rule='rule family=ipv4 source address=xxx.xxx.xx.x/32 reject'
firewall-cmd --permanent --zone=<name> --add-rich-rule='rule family=ipv4 source address=xxx.xxx.xx.x/24 port=xxxx-xxxx protocol tcp <accept|reject|drop>'
firewall-cmd --add-rich-rule='rule service name=ftp limit value=2/m accept'
firewall-cmd --permanent --zone=<name> --add-masquerade
firewall-cmd --permanent --zone=<name> --add-rich-rule='rule family=ipv4 source address=xxx.xxx.xx.x/24 masquerade'

Example

firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=172.31.119.123 forward-port port=443 protocol=tcp to-port=22'
firewall-cmd --permanent --zone=home --add-rich-rule='rule family=ipv4 source address=172.31.44.157 service name="http" log level=notice

Logging

Port Forwarding (Rich rule & Normal Rule)

firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=xxx.xxx.xx.x/24 forward-port port=xx protocol=tcp to-port=xx to-addr=xxx.xx.xx.x'
firewall-cmd --permanent --zone=<name> --add-forward-port=port=<xxxx>:proto=<tcp>[:toport=<xxxx>:toaddr=<xxx.xxx.xx.x>]
firewall-cmd --<remove-rich-rule=RULE|query-rich-rule=RULE|list-rich-rules>

SELinux

man 8 semanage-fcontext

Install setools-console and list context

yum -y install setools-console
seinfo -t | grep <string>

SELinux Policy Management port mapping tool

semanage port -l

semanage port -<a|d|m> -t http_port_t -p tcp <88>

m=same as removing & adding

yum -y install selinux-policy-devel

Create or update the manual page index caches

mandb

Same as apropos, search the manual page names and descriptions:

man -k _selinux

Generate SELinux man pages sepolicy-manpage

sepolicy manpage -a

Install packages for troubleshooting SELinux policy denials and violations

yum install -y setroubleshoot-server setools

DNS

man unbound.conf

This is the old way of doing this, now handled by nmcli

vim /etc/resolv.conf

host -v -t A example.com
host -v -t AAAA a.root-servers.net
host -v -t A ipa-ca-server0.example.com
host -v -t PTR 172.25.0.10
host -v -t PTR 2001:503:ba3e::2:30
host -v -t <NS|SOA|MX|TXT> example.com
host -v -t SRV _ldap._tcp.server0.example.com

Installation

yum -y install unbound
systemctl start unbound
systemctl enable unbound

Configuration

vim /etc/unbound.conf

Default is localhost

    interface: 0.0.0.0

Default does not accept any connections

    access-control: 172.25.0.0/24 allow

dot stands for the root domain

    forward-zone:
        name: "."

Forward query to what DNS

        forward-addr: 172.25.254.254

Domains not configured with DNSSEC

    domain-insecure: example.com

unbound-checkconf
systemctl restart unbound
firewall-cmd --permanent --add-service=dns
firewall-cmd --reload
unbound-control dump_cache > dump.out
unbound-control load_cache < dump.out
unbound-control flush_zone <example.com>
unbound-control flush <www.example.com>
getent hosts <example.com>
gethostip <example.com>
dig A <example.com>
dig @<dns.example.com> A <www.example.com>
dig +tcp A <example.com>
dig +dnssec DNSKEY <example.com>

NTP

yum install -y ntp
systemctl enable ntpd
ntpdate pool.ntp.org
systemctl start ntpd
ntpq -p
ntpstat

Chrony

yum install -y chrony
systemctl enable chronyd
systemctl start chronyd
chronyc tracking
chronyc sources -v
chronyc sourcestats -v
ntpdate pool.ntp.org

POSTFIX AS NULL CLIENT

man 5 postconf

/usr/share/doc/postfix-2.10.1/README_FILES/STANDARD_CONFIGURATION_README

cp /etc/postfix/main.cf ~/main.cf.orig

Needs a change of 6 variables

vim /etc/postfix/main.cf

Which NIC Postfix listens on for incoming/outgoing messages, can be “all”

    inet_interfaces = loopback-only

    inet_interfaces = all

e-mails will appear to come from this domain

    myorigin = clientX.example.com

Forward all messages to this email server

    relayhost = [server.example.com]

Which domains the mail server is an end point for, email address to a domain listed here is rejected

    mydestination =

    local_transport = error: local delivery disabled

Allo relay from these networks

    mynetworks = 127.0.0.0/8, [::1]/128

postfix check
systemctl restart postfix
postconf <-e> 'VAR = VAL'

Show configuration parameters that have explicit name=value settings in main.cf

postconf -n

firewall-cmd --permanent --add-service=smtp
postqueue -<p|f>
mail -s "serverX null client" [email protected] null client test
[ENTER].[ENTER]

Postconf Configuration

postconf -e "relayhost=[smtp1.example.com]"
postconf -e "inet_interfaces=loopback-only"
postconf -e "mynetworks=127.0.0.0/8 [::1]/128"
postconf -e "myorigin=desktop1.example.com"
postconf -e "mydestination="
postconf -e "local_transport=error: local delivery disabled"

Gmail Specific Settings

relayhost = [smtp.gmail.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_password
smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt
smtp_sasl_security_options = noanoymous
smtp_sasl_tls_security_options = noanoymous

iSCSI

Targets - server creating

man 8 targetcli

yum -y install targetcli

LVM:

fdisk <device> => type 8e
pvcreate <partition>
vgcreate <vgname> <partition>
lvcreate -n <lvname> -L <size> <vgname>

Example: lvcreate (-l 100%FREE)

fdisk /dev/vdb => type 8e
pvcreate /dev/vdb1
vgcreate iSCSI_vg /dev/vdb1
lvcreate -n disk1_lv -L 100m iSCSI_vg

targetcli
systemctl start|enable target
cd /backstores
block/ create <block1> /dev/iSCSI_vg/disk1_lv
block/ create <block2> /dev/vdb2
block/ create <file1> /root/disk1_file 100M
cd /iscsi
create iqn.2017-07.com.example:server
cd iqn.2017-07.com.example:server/tpg1
acls/ create iqn.2017-07.com.example:client
luns/ create /backstores/block/block1
luns/ create /backstores/block/block2
luns/ create /backstores/fileio/file1
portals/ create 172.25.0.11

Or portals/ create without IP address

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

Authentication

cd acls/iqn.2017-07.com.example:client set auth userid=lunuser set auth password=password

Targets - client accessing

/usr/share/doc/iscsi-initiator-utils-6.2.0.873 - Section 7.3 - node.startup

man 8 iscsiadm

yum -y install iscsi-initiator-utils
vim /etc/iscsi/initiatorname.iscsi (InitiatorName=iqn.2017-07.com.example:client)
systemctl restart iscsi
systemctl enable iscsi
iscsiadm -m discovery -t sendtargets -p 172.25.0.11:3260

Don’t need port if it’s default

If we want to add Authentication:

vim iscsid.conf

And uncomment:

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

iscsiadm -m node -T iqn.2017-07.com.example:server -p 172.25.0.11 -l

iscsiadm -m node -T iqn.2017-05.com.example:server1 -p 127.25.1.11:3260 -o update -n node.startup -v automatic
lsblk --scsi
fdisk /dev/sda
mkfs.xfs/ext4
blkid /dev/sda1 >> /etc/fstab
vim /etc/fstab
UUID=xxxxx-xxxxx-xxxxx /mnt/iscsi xfs _netdev 0 2

_netdev is important and it means mount after networking initialized.

Check if Disk is in RO Mode:

lsblk | egrep "NAME|sda"

Other Checks:

mount -av
cd /var/lib/iscsi/nodes; ls -lR
iscsiadm -m session -P 3

Targets - client disconnecting

rm /var/lib/iscsi/nodes/*iqn*
iscsiadm -m node -T iqn.2017-07.com.example:server -p 172.25.0.11 -u
iscsiadm -m node -T iqn.2015-10.com.example:server -p 172.25.0.11 -o delete
systemctl restart iscsi
lsblk

Reboot Server when iSCSI

umount /mnt/iscsi
systemctl stop iscsi

Install a Kerberos Server

yum install -y krb5-server krb5-workstation pam_krb5

Change /etc/hosts with network servers IP or add a DNS

cd /var/kerberos/krb5kdc/
vi kdc.conf

Change realms from EXAMPLE.COM to your domain Uncomment master_key_type = aes256-cts to use with kerberos 5 Also add: default_principal_flags = +preauth

vim /etc/krb5.conf Change EXAMPLE.COM to your domain

vim /var/kerberos/krb5kdc/kadm5.acl

Change */[email protected] to your domain

kd5b_util create -s -r EXAMPLE.COM

Enter Master Key

systemctl enable krb5kdc kadmin
systemctl start krb5kdc kadmin

kadmin.local

addprinc root/admin
addprinc krbtest
addprinc -randkey host/server.example.com
ktadd host/server.example.com

vim /etc/ssh/ssh_config

GSSAPIAuthentication yes
GSSAPIDelegationCredentials yes

systemctl reload sshd

authconfig --enablekrb5 --update

cd /etc/firewalld/services
vim kerberos.xml

<?xml version="1.0" encoding="utf-8"?>
<service>
  <short>Kerberos</short>
  <description>Kerberos network authentication protocol server</description>
  <port protocol="tcp" port="88"/>
  <port protocol="udp" port="88"/>
  <port protocol="tcp" port="749"/>
</service>

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

useradd krbtest
su - krbtest
kinit
klist
ssh server

Install a Kerberos Client

yum install -y krb5-workstation pam_krb5

vim /etc/krb5.conf

Change EXAMPLE.COM to your domain (Same configuration as the server). You can copy the /etc/krb5.conf from the Server.

useradd krbtest
kadmin

addprinc -randkey host/client.example.com
ktadd host/client.example.com

vim /etc/ssh/ssh_config

GSSAPIAuthentication yes
GSSAPIDelegationCredentials yes

systemctl reload sshd

authconfig --enablekrb5 --update

su - krbtest
kinit
klist
ssh server

Produce and Deliver Reports on System Load (Processor, Memory, Disk, and Network)

dstat

yum -y install dstat

Show CPU dstat -c

Show Disk dstat -d

Show Memory dstat -m

Show Network dstat -n

Show Paging dstat -g

System Stats dstat -y

Processes dstat -p

RW Requests dstat -r

Show SWAP Statistics dstat -s

Output to File (t for Time) dstat -tcdm --output dstat.csv

sysstat

Creates historic reports

yum -y install sysstat

iostat
pidstat

cd /etc/sysconfig
ls sysstat sysstat.ioconf

cd /etc/cron.d
ls sysstat

Logs are created under /var/log/sa

Generate Reports with Sysstat

See Report:

sadf -s 01:00:00 -e 23:59:00 /var/log/sa/sa07

Export Report:

sadf -d /var/log/sa/sa07 -- -urd -n DEV

NFS

man exports

Server - Insecure

yum -y install nfs-utils
systemctl start rpcbind
systemctl enable rpcbind
systemctl start nfs-server
systemctl enable nfs-server
mkdir /myshare
chown nfsnobody /myshare
vim /etc/exports
    /myshare client.example.com(rw)
    /myshare *.example.com
    /myshare server[0-20].example.com
    /myshare 172.25.0.0/16
    /myshare 172.25.11.10(rw,no_root_squash) *.example.com(ro)

no_root_squash

By default, root on a NFS client acts as user nfsnobody by the NFS server. That is, if root attempts to access a file on a mounted export, the server will treat it as an access by user nfsnobody instead. This is a security measure that can be problematic in scenarios using NFS exports as “/” by diskless clients and root needs to act as root.

exportfs -r<av>
firewall-cmd --permanent --add-services=nfs
firewall-cmd --reload
showmount -e <server>

Client - Insecure

yum -y install nfs-utils
systemctl start rpcbind
systemctl enable rpcbind
systemctl enable nfs
mount -t nfs server.example.com:/myshare /mnt/nfs
vim /etc/fstab
    nfserver:/sharename /mountpoint nfs _netdev,rw 0 0

Server - Secure

wget -O /etc/krb5.keytab http://server.example.com/server.keytab
klist -k; kinit <user>
vim /etc/sysconfig/nfs
    (RPCNFSDARGS="-V 4.2")
systemctl restart nfs-server
systemctl restart nfs-secure-server
systemctl enable nfs-secure-server
vim /etc/exports
    /mysecureshare client.example.com(sec=krb5p,rw)

Uses nfsnobody, needs boolean nfsd_anon_write sec=none Using UID/GUIS linux file permissions [default] sec=sys Kerberos and then Linux file permissions apply sec=krb5 Adds checksums to the data transfers sec=krb5i ADd encryption sec=krb5p

exportfs -r<av>
firewall-cmd --permanent --add-services=nfs
firewall-cmd --reload

Client - Secure

yum -y install nfs-utils

Important

systemctl start nfs-secure
systemctl enable nfs-secure

wget -O /etc/krb5.keytab http://server.example.com/client.keytab
mount -o sec=krb5p,v4.2 server.example.com:/mysecureshare /mnt/nfs
vim /etc/fstab
    serverx:/securenfs /mnt/secureshare nfs defaults,v4.2,sec=krb5p 0 0
mount -av

SELinux for NFS

man 8 nfsd_selinux

Context Default:

nfs_t - NFS server to access share, both readable and writable
public_content_t - NFS and other services to read contents of the share

For writable, change context: public_content_rw_t

Doesn’t survive FS relabel: chcon –t public_content_t /securenfs/testfile.txt

Booleans

nfs_export_all_ro [default=on],
nfs_export_all_rw [default=on],
nfsd_anon_write [default=off]. It must be enabled for public_content_rw_t e.g.:

setsebool -P nfsd_anon_write=on

Provide NFS network shares to specific clients

NFS Server Configuration

Install the file-server package group:

yum groupinstall -y file-server

Add a new service to the firewall:

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

Note: NFSv4 is the version used at the exam and doesn’t need any extra firewall configuration. Beyond the exam objectives, if you plan to use NFSv3, you will also need to run these commands:

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

Reload the firewall configuration:

firewall-cmd --reload

Activate the NFS services at boot:

systemctl enable rpcbind nfs-server

Note: The nfs-idmap/nfs-idmapd (changes happened with RHEL 7.1) and nfs-lock services are automatically started by the nfs-server service. nfs-idmap/nfs-idmapd is required by NFSv4 but doesn’t allow you any UID/GID mismatches between clients and server. Used when setting ACL by names or to display user/group names. All permission checks are still done with the UID/GID used by the server.

Start the NFS services:

systemctl start rpcbind nfs-server

Note1: By default, 8 NFS threads are used (RPCNFSDCOUNT=8 in the /etc/sysconfig/nfs file). This should be increased in a production environment to at least 32.

Note2: Optionally, to enable SELinux Labeled NFS Support, edit the /etc/sysconfig/nfs file and paste the following line (source): RPCNFSDARGS=”-V 4.2″

Create directories to export and assign access rights:

mkdir -p /home/tools
chmod 0777 /home/tools
mkdir -p /home/guests
chmod 0777 /home/guests

Assign the correct SELinux contexts to the new directories:

yum install -y setroubleshoot-server
semanage fcontext -a -t public_content_rw_t "/home/tools(/.*)?"
semanage fcontext -a -t public_content_rw_t "/home/guests(/.*)?"
restorecon -R /home/tools
restorecon -R /home/guests

Note: The public_content_rw_t context is not the only available, you can also use the public_content_ro_t (only read-only) or nfs_t (more limited) contexts according to your needs.

Check the SELinux booleans used for NFS:

semanage boolean -l | egrep "nfs|SELinux"

SELinux boolean                State  Default Description
xen_use_nfs                    (off  ,  off)  Allow xen to use nfs
virt_use_nfs                   (off  ,  off)  Allow virt to use nfs
mpd_use_nfs                    (off  ,  off)  Allow mpd to use nfs
nfsd_anon_write                (off  ,  off)  Allow nfsd to anon write
ksmtuned_use_nfs               (off  ,  off)  Allow ksmtuned to use nfs
git_system_use_nfs             (off  ,  off)  Allow git to system use nfs
virt_sandbox_use_nfs           (off  ,  off)  Allow virt to sandbox use nfs
logrotate_use_nfs              (off  ,  off)  Allow logrotate to use nfs
git_cgi_use_nfs                (off  ,  off)  Allow git to cgi use nfs
cobbler_use_nfs                (off  ,  off)  Allow cobbler to use nfs
httpd_use_nfs                  (off  ,  off)  Allow httpd to use nfs
sge_use_nfs                    (off  ,  off)  Allow sge to use nfs
ftpd_use_nfs                   (off  ,  off)  Allow ftpd to use nfs
sanlock_use_nfs                (off  ,  off)  Allow sanlock to use nfs
samba_share_nfs                (off  ,  off)  Allow samba to share nfs
openshift_use_nfs              (off  ,  off)  Allow openshift to use nfs
polipo_use_nfs                 (off  ,  off)  Allow polipo to use nfs
use_nfs_home_dirs              (off  ,  off)  Allow use to nfs home dirs
nfs_export_all_rw              (on   ,   on)  Allow nfs to export all rw
nfs_export_all_ro              (on   ,   on)  Allow nfs to export all ro

Note1: The State column respectively shows the current boolean configuration and the Default column the permanent boolean configuration.

Note2: Here we are interested in the nfs_export_all_rw, nfs_export_all_ro and potentially use_nfs_home_dirs booleans.

Note3: The nfs_export_all_ro boolean allows files to be shared through NFS in read-only mode but doesn’t restrict them from being used in read-write mode. It’s the role of the nfs_export_all_rw boolean to allow read-write mode.

If necessary, assign the correct setting to the SELinux booleans:

setsebool -P nfs_export_all_rw on
setsebool -P nfs_export_all_ro on
setsebool -P use_nfs_home_dirs on

Edit the /etc/exports file and add the following lines with the name (or IP address) of the client(s):

/home/tools nfsclient.example.com(rw,no_root_squash)
/home/guests nfsclient.example.com(rw,no_root_squash)

Note: Please, don’t put any space before the opening parenthesis, this would change the meaning of the line!

Export the directories:

exportfs -avr

systemctl restart rpcbind
systemctl restart nfs-server

Note: This last command shouldn’t be necessary in the future. But, for the time being, it avoids rebooting.

Check your configuration:

showmount -e localhost

Note: You can test what is exported by the NFS server from a remote client with the command showmount -e nfsserver.example.com but you first need to stop Firewalld on the NFS server (or open the 111 udp and 20048 tcp ports on the NFS server).

NFS Client Configuration

On the client side, the commands are:

yum install -y nfs-utils
mount -t nfs nfsserver.example.com:/home/tools /mnt

Kerberos NFS Server Configuration

Before adding the Kerberos configuration, set up the NFS server NFS Server Configuration

Then, you will have to add the Kerberos client configuration

Finally, add the specific NFS part to the principals:

kadmin
Authenticating as principal root/[email protected] with password.
Password for root/[email protected]: kerberos
kadmin:  addprinc -randkey nfs/nfsserver.example.com
WARNING: no policy specified for host/[email protected]; defaulting to no policy
Principal "host/[email protected]" created.

Create a local copy stored by default in the /etc/krb5.keytab file:

kadmin:  ktadd nfs/nfsserver.example.com
kadmin:  quit

authconfig --enablekrb5 --update

Edit the /etc/exports file and add the option sec=krb5 (or the option that you want, see note):

/home/tools nfsclient.example.com(rw,no_root_squash,sec=krb5)
/home/guests nfsclient.example.com(rw,no_root_squash,sec=krb5)

Note1: The sec option accepts four different values: sec=sys (no Kerberos use), sec=krb5 (Kerberos user authentication only), sec=krb5i (Kerberos user authentication and integrity checking), sec=krb5p (Kerberos user authentication, integrity checking and NFS traffic encryption). The higher the level, the more you consume resources.

Note2: If you want to use sec=sys (no Kerberos use), you also need to run setsebool -P nfsd_anon_write 1

Export the new configuration:

exportfs -avr

Check your configuration:

showmount -e localhost

Activate at boot and start the nfs-secure-server service (RHEL 7.0):

systemctl enable nfs-secure-server && systemctl start nfs-secure-server

Note: If you want to get more information in the /var/log/messages file, edit the /etc/sysconfig/nfs file, assign the “-vvv” string to the RPCIDMAPDARGS/RPCSVCGSSDARGS variables and restart the nfs-idmap/nfs-secure-server daemons.

Kerberos NFS Client Configuration

kadmin
Authenticating as principal root/[email protected] with password.
Password for root/[email protected]: kerberos
kadmin:  addprinc -randkey nfs/nfsclient.example.com
WARNING: no policy specified for host/[email protected]; defaulting to no policy
Principal "host/[email protected]" created.

Create a local copy stored by default in the /etc/krb5.keytab file:

kadmin:  ktadd nfs/nfsclient.example.com
kadmin:  quit

Activate at boot and start the nfs-secure service (RHEL 7.0):

systemctl enable nfs-secure && systemctl start nfs-secure

Activate at boot and start the nfs-client target (RHEL 7.1 and after):

systemctl enable nfs-client.target && systemctl start nfs-client.target

Note1: Since RHEL 7.1, the nfs-secure service automatically starts if there is a /etc/krb5.keytab file.

Note2: If you want to get more information in the /var/log/messages file, edit the /etc/sysconfig/nfs file, assign the “-vvv” string to the RPCIDMAPDARGS/RPCGSSDARGS variables and restart the nfs-idmap/nfs-secure daemons.

Note3: With the RHEL 7.3 release, the Systemd init system is able to use aliases. For example, the nfs.service is a symbolic link/alias to the nfs-server.service service file. This enables, for example, using the systemctl status nfs.service command instead of systemctl status nfs-server.service. Previously, running the systemctl enable command using an alias instead of the real service name failed with an error.

Mount the remote directory:

mount -t nfs4 -o sec=krb5 nfsserver.example.com:/home/tools /mnt

Note1: If you get the error message “mount.nfs4: an incorrect mount option was specified”, check that you started the correct daemons.

Note2: It is not necessary to specify the rw option, it is done by default.

Note3: You can test what shares are exported by the NFS server with the command showmount -e nfsserver.example.com but you first need to stop Firewalld on the NFS server (or open the 111 udp and 20048 tcp ports on the NFS server).

Note4: If you don’t specify the sec option, the security mechanism will be negotiated transparently with the remote server.

To permanently set up the mount, paste the following line in the /etc/fstab file:

nfsserver.example.com:/home/tools /mnt nfs4 sec=krb5

Switch to the user1 user:

su - user1

Create a Kerberos ticket:

kinit

Create a file called testFile:

cd /mnt
echo "This is a test." > testFile

Check the result:

ls -l

SMB

man 5 smb.conf

Server

yum -y install samba samba-client
cp /etc/samba/smb.conf ~/smb.conf.orig
vim /etc/samba/smb.conf

Defaults that do not specifically define certain items

    [global]
        workgroup=WORKGROUP

User-level security where user must be logged in, requires samba password

        security=user
        hosts allow=172.25. .example.com

e.g. xxx.xx.x.x EXCEPT xxx.xx.x.x, e.g. xxx.xx.x.x/255.0.0.0; can be also hosts deny=xxx.xx.x.x

Name of the Share

    [myshare]
        path=/sharedpath
        writable=<yes|no>
        write list=<user>

Even if writable is no

        valid users=<blank>|<user>|@management|+users

By default empty, all users have access to the share. Specifies who can log in to the share.

    [homes]
        read only=no
    [printers]

testparm
groupadd <group>
useradd -s /sbin/nologin -G <group> <user>

Change a user's SMB password

smbpasswd -<a|x> <user>

List all samba accounts configured on the server

pdbedit –Lv

or

cat /var/lib/samba/private/smbpasswd

systemctl reload smb nmb

systemctl enable smb nmb
firewall-cmd --permanent --add-service=samba
firewall-cmd --reload

Same as chmod u+rw,g+rws,o+rx /sharedpath chmod 2775 /sharedpath

Another Example

[global]
  workgroup      = MYLABSERVER
  server string  = 172.31.3.243
  hosts allow    = 127. 172.31.106.46
  interfaces     = lo eth0 172.31.36.
  passdb backend = smbpasswd
  security       = user
  log file       = /var/log/samba/%m.log
  max log size   = 5000
[sambashare]
  comment        = /sambashare
  browsable      = yes
  path           = /sambashare
  public         = yes
  valid users    = user1
  write list     = user1
  writable       = yes
[smbgroup]
  comment        = /smbgroup
  browsable      = yes
  path           = /smbgroup
  public         = no
  valid users    = @smbgrp
  write list     = @smbgrp
  writable       = yes
  force group    = +smbgrp
  create mask    = 0770

Test Samba Connectivity on Server

smbclient -L //localhost -U user1

Client - Single User

yum -y install cifs-utils
vim /root/credentials.txt
    username=<user>
    password=<password>

Same as chmod u+r credentials.txt chmod 0400 /root/credentials.txt

By default it uses “sec=ntlmssp mount -o <username=<user>,password=<password>,uid=1004,gid=1004 | credentials=credentials.txt> -t cifs //server.example.com/<sharename> /mnt/smb

smbclient -L //server.example.com -U user1

Client - Multiuser

yum -y install cifs-utils
useradd <user>
su - <user>

Manage NTLM credentials in the keyring) cifscreds <add|update|clear|clearall> -u <user> <server.example.com>

User must exist on the client and have corresponding SMB account on the server

mount -o multiuser,sec=ntlmssp,username=<user>,credentials=<multiuser_file.txt> //server.example.com/<sharename> /mnt/multiuser
    vim /root/multiuser_file.txt
        username=<user_with_minimal_permissions_on_the_share>
        password=<password>
    vim /etc/fstab
        //serverX/sambashare /mnt/multiuser cifs
        credentials=/root/multiuser.txt,multiuser,sec=ntlmssp 0 0
mount -av
smbclient -L server.example.com –U <user>

SELinux for SMB

man 8 samba_selinux

Context

samba_share_t - SMB to access the share
public_content_t & public_content_rw_t - accessible by other services as well

Boolean

samba_export_all_ro
samba_export_all_rw
samba_share_nfs
smbd_anon_write [default=off] must be enabled if public_content_rw_t is applied.
boolean for home dirs:
- samba_enable_home_dirs [default=off] on the server
- use_samba_home_dirs [default=off] on the client

Example: getsebool -a | grep -i <boolean_name>

Permanent change to SE policy file on disk setsebool -P samba_enable_home_dirs=on

Special Permission	Effect on files	Effect on directories
u+s (suid) 4xxx	Executes as user who owns, not who runs	---
g+s (sgid) 2xxx	Executes as group that owns, not who runs	New files have group owner match group owner of the dir
o+t (sticky) 1xxx	---	Users who can write to the dir can remove their own files

MARIADB

MariaDB [(none)]> help

yum -y groupinstall mariadb mariadb-client
systemctl start mariadb
systemctl enable mariadb

Set root passwd,remove anonym,disallow root login,remove testdb mysql_secure_installation

vim /etc/my.cnf
    [mysqld]

If blank, ipv4 is allowed

        bind-address = <::|0.0.0.0|blank>

1=not even localhost can connect, only socket

        skip-networking = <1|0>

Port number 3306 by default

        port

firewall-cmd --permanent --add-rule=mysql
firewall-cmd --reload
mysql -u <root> -h <hostname> -p
create|show|drop database <name>;
use <name>;

Managing Users and Access Rights

MariaDB [(none)]> help grant

    create user <user>@'<%|192.168.1.%|localhost>' identified by '<password>';
mysql -u <user> -h <hostname> -p
    grant select on <database.table> to <user>@<hostname>;
    grant select on <database.*> to <user>@<hostname>;
    grant select on <*.*> to <user>@<hostname>;
    grant <create,alter,drop> on <database.*> to <user>@<hostname>;
    grant all privileges on <*.*> to <user>@<hostname>;
    revoke <select,update,delete,insert> on <database.table> from <user>@<hostname>;
    flush privileges;
    show grants for <user>@<hostname>;
    drop user <user>@<hostname>;

Backup - Logical

mysqldump -u root -p <dbname> > /tmp/dbname.dump
mysqldump -u root -p --<all-databases|add-drop-tables|no-data|lock-all-tables|add-drop-databases> > /tmp/all.dump

--all-databases will include all user information

Backup - Physical

mysqladmin variables | grep datadir
cat /etc/my.cnf | grep -i datadir
df /var/lib/mysql

/dev/mapper/vg0-mariadb shows 'vg0' is volume group and 'mariadb' is logical volume name

vgdisplay vg0 | grep free
tty0: mysql -u root -p
    tty0: flush tables with read lock;
tty1: lvcreate -L20G -s -n mariadb-backup /dev/vg0/mariadb

-s=snapshot, must be large enough to hold the backup

tty0: unlock tables;
mkdir /mnt_snapshot
mount /dev/vg0/mariadb-backup /mnt_snapshot
tar cvzf mariadb_backup.tar.gz /mnt_snapshot/var/lib/mysql
umount /mnt_snapshot
lvremove /dev/vg0/mariadb-backup

Restore - Logical

mysql -u root -p <dbname> < /backup/dbname.dump

Restore - Physical

systemctl stop mariadb
mysqladmin variables | grep datadir
rm -rf /var/lib/mysql/*
tar xvzf mariadb_backup.tar.gz /var/lib/mysql

Queries

    show databases;
    create table <scientists> (Number int,FirstN varchar(20),LastN varchar(20));
    select * from product;
    select * from <table1>, <table2> where ‘value1=1’ and ‘value2=2’;
    show tables;
    describe|delete|insert|rename|select|update <table>;
    insert into <product> (name,price) values ('oracle',1000);

Do not insert values into "Auto Increment" fields

    delete from <product> where <id=1>;
    delete from <category> where name like 'Memory';
    update <product> set <price=999> where <id=1>;
    select name,price,stock from product;
    select * from product where price > 90;
    select <field> from <table> where <field>="x";
    exit;

APACHE

http://localhost/manual

yum -y install httpd httpd-manual

grep -v '^#' /etc/httpd/conf.d/httpd.conf > /etc/httpd/conf.d/httpd_without_comments.conf
cp /etc/httpd/conf/httpd.conf ~/httpd.conf.orig

Global server configuration

vim /etc/httpd/conf/httpd.conf Where are the config files

    ServerRoot "/etc/httpd"

Can be 1.2.3.4:80, multiple ports must be specified on separate lines

    Listen 80

If multiple are present, they will be alphabetically included

    Include conf.modules.d/*.conf

    User apache
    Group apache
    ServerAdmin root@localhost

Directives specific to the dir and all descendent dirs

    <Directory />

.htaccess will not be used

        AllowOverride none

Refuse to serve content from dir

        Require all denied
    </Directory>

Where apache looks for files

        DocumentRoot "/var/www/html"

    <Directory  "/var/www/">
        AllowOverride none
        Require all granted
    </Directory>
    <Directory "/var/www/html">
        Options Indexes FollowSymLinks
        AllowOverride none
        Require all granted
    </Directory>

If this module is loaded, what happens

    <IfModule dir_module>

This file will be used when the directory is requested

        DirectoryIndex index.html
    </IfModule>

Same as directory but for file wildcards

<Files ".ht*">
        Require all denied
    </Files>

IT will go for /etc/httpd/logs/error_log, which is symlink to /var/log/httpd/error_log

    ErrorLog "logs/error_log"

    LogLevel warn
    CustomLog "logs/access_log" combined

Can be disabled by AddDefaultCharset Off

    AddDefaultCharset UTF-8

Same as Regular include

    IncludeOptional conf.d/*.conf (same as regular include)

Validate the config files httpd -t

systemctl enable httpd
systemctl start httpd
firewall-cmd --permanent --add-service=http --add-service=https
firewall-cmd --reload
semanage port -l | grep '^http_'

New DocumentRoot for group 'webmasters'

Same as chmod u+rw, g+rws, o+rx /new/web

mkdir -p -m 2775 /new/web

groupadd webmasters
chgrp webmasters /new/web
chmod 2775 /new/web

X=Keeps executable settings,directories allow directory search,x=executable

setfacl -R -m g:webmasters:rwX /new/web
setfacl -R -m d:g:webmasters:rwX /new/web

Rules are already in place to relabel /srv/*/www

semanage fcontext -a -t httpd_sys_content_t "/new/web(/.*)?"

Resets the context on the files AFTER you create them

restorecon -Rv /new/web

systemctl reload httpd

Private directory protected by password

<Directory /var/www/private>

Set basic authentication

AuthType Basic
AuthName "This site is password protected. Enter password:"

Specifies the file with user/passwd

AuthUserFile /etc/httpd/conf/userpasswords
Require user user1

Or valid-user for anyone in the userpasswords file

</Directory>
htpasswd –bc /etc/httpd/conf/userpasswords user1 p4ssw0rd
chmod 0640 /etc/httpd/conf/userpasswords
chgrp apache /etc/httpd/conf/userpasswords

Together with AuthUserFile, you can use AuthGroupFile and Require group. Content of the group file is: cat /etc/httpd/conf/grouppasswords: groupname: user1 user2 user3. These users must be in userpasswords file.

Virtual Hosts

vim /etc/httpd/conf.d/00-site1.conf

This block provides access to Document Root further down

    <Directory /srv/site1/www>
        Require all granted
        AllowOverride none
    </Directory>

This block must be considered for all connections on 192.168.0.1:80, can be default:80 or *:80 which will ALWAYS match for regular http traffic, effectively disabling the main server config from ever being used on port 80.

    <VirtualHost 192.168.0.1:80>

Applies for within this Virtual Host

        DocumentRoot /srv/site1/www

Name-based virtual hosting, if multiple virtual hosts are defined, the one where hostname matches this will be used, it is best to always explicitly use this. It doesn’t need to exist, if you need “match anything” – e.g. all other domains types of VirtualHosts

        ServerName site1.example.com[:80]

If the virtual host needs to be used for more than one domain name, wildcards can be used e.g. *.example.com

        ServerAlias site1
        ServerAdmin [email protected]
        ErrorLog "logs/site1_error_log"
        CustomLog "logs/site1_access_log" combined
    </VirtualHost>

httpd –D DUMP_VHOSTS
semanage fcontext -a -t httpd_sys_content_t "/srv/site1/www(/.*)?"
restorecon -Rv /srv/site1/www

If there are multiple catch-all VirtualHosts, they will be executed alphabetically (e.g. 00-default.conf,default.conf,vhost.conf).

How the server selects the proper name-based virtual host? When a request arrives, the server will find the most specific virtual host argument based on IP/port used by the request. If there is more than one containing the best-match, Apache will further compare the ServerName and ServerAlias directives to the server name present in the request. If no matching ServerName/ServerAlias is found in the set of virtual hosts, then the first listed virtual host that matches will be used.

Any request that does not match existing virtual host is handled by the global server configuration /etc/httpd/conf/httpd.conf, regardless of hostname/ServerName. When you add virtual host to an existing server and the virtual host match preexisting IP/port, request will now be handled virtual host. In this case, it is wise to create default virtual host with ServerName matching the base server.

Access Control Directives

<RequireAll></RequireAll> - none must fail and at least one must succeed <RequireAny></RequireAny> - one or more must succeed <RequireNone></RequireNone> - none must succeed

If is not enclosed in directives, is automatically <RequireAny>

Examples

1. Address is an IP, partial IP, network/mask, network/CIDR, ipv4/ipv6

<RequireAll>
      Require all granted
Require not ip 10.252.46.125
</RequireAll>

2. Address is FQDN or part of it, multiple may be provided

<RequireAll>
Require all granted
Require not ip 192.168.2.1
Require not host phishers.example.com moreidiots.example
Require not host gov
</RequireAll>

3. Require All Denied

Require all denied
Require local

4. Allows specific hostname

Require host test.example.com

5. Can be username / UID

Require User John

6. Can be groupname /GID

Require not user badjohn

7. Require IP

Require ip 192.168.15.2

SSL/TLS

yum -y install crypto-utils mod_ssl
genkey <www.example.com>
cp /etc/httpd/conf.d/ssl.conf ~/ssl.conf.orig
grep -v '^#' /etc/httpd/conf.d/ssl.conf > /etc/httpd/conf.d/ssl_without_comments.conf
vim /etc/httpd/conf.d/ssl.conf
    Listen 443 https

If the private key uses passphrase

    SSLPassPhraseDialog exec:/usr/libexec/httpd-ssl-pass-dialog
    <VirtualHost _default_:443>
        SSLEngine on

ServerName www.example.com[:443] Public Key

        SSLCertificateFile /etc/pki/tls/certs/www.example.com.crt

Private Key

        SSLCertificateKeyFile /etc/pki/tls/certs/www.example.com.key

Copy of all CA Certificates

        SSLCertificateChainFile /etc/pki/tls/certs/example-ca.crt
        DocumentRoot /var/www/html
    </VirtualHost>

This is the Default

ls -Zd /etc/pki/tls/
semanage fcontext -a -t cert_t "/etc/pki/tls(/.*)?"
restorecon -Rv /etc/pki/tls/

Same as chmod u+rw *.key

chmod 0600 /etc/pki/tls/private/*.key

same as chmod u+rw,g+r,o+r *.crt

chmod 0644 /etc/pki/tls/certs/*.crt

HSTS - strict transport security

    <VirtualHost *:80>
    ServerName...;ServerAlias...;DocumentRoot...
    Header always set Strict-Transport-Security "max_age=15768000"
    RewriteEngine on
    RewriteRule ^(/.*)$ https://%{HTTP_POST}$1 [redirect=301]
    <VirtualHost>

Dynamic content

1. CGI

    vim /etc/httpd/conf/httpd.conf

First parameter is part of the URL, second is the location of the script.

        ScriptAlias /cgi-bin/ "/var/www/cgi-bin/"

<Directory /var/www/html>
    Options none
    Require all granted
</Directory>

SELinux fcontext: httpd_sys_script_exec_t, httpd_enable_cgi

2. PHP

    yum -y install mod_php php php-mysql
        <FilesMatch \.php$>
            SetHandler application/x-httpd-php
        </FilesMatch>
        DirectoryIndex index.php

3. Python

    yum -y install mod_wsgi
    vim /etc/httpd/conf/httpd.conf

A request for www.example.com/myapp will cause the server to run the WSGI application defined in /srv/my.py

    WSGIScriptAlias /myapp "/srv/my.py"

SELinux fcontext: httpd_sys_content_t

SELinux in Apache

man 8 httpd_selinux

semanage port -l | grep '^http_'

Non-Standard HTTP Ports

semanage port -a -t http_port_t -p tcp 88

semanage fcontext -a -t httpd_sys_content_t "/srv/site1/www(/.*)?"

Not before files are present

restorecon -Rv /srv/site1/www

Apache SELinux Context

httpd_sys_content_t - Dirs where Apache is allowed to access httpd_sys_content_rw_t - Dirs where Apache is allowed to read/write httpd_sys_script_exec_t - dirs that contain executable scripts cert_t - Dirs where Apache is allowed to read SSL certificates

Apache SELinux Booleans

httpd_unified [default=off] - Simplified/unified policy when turned on

httpd_enable_cgi [default=on] - Allowed to run scripts

httpd_tty_comm [default=off] - Apache is allowed to access TTY, switch on when using private key with passkey

httpd_can_network_connect_db [default=off] - If the database is on remote host

httpd_can_network_connect [default=off] - If the known port number is used for db connection

httpd_anon_write [off], httpd_sys_script_anon_write [off] – If directory that is using public_content_rw_t is being used by Apache

SHELL ENVIRONMENT

Global

    /etc/profile
    /etc/profile.d/*.sh
    /etc/bashrc

User

    ~/.bash_profile, .bash_login, .profile
    ~/.bashrc

Profiles are for setting and exporting of environment variables, as well as running commands that should run upon login. Usually, profiles are executed in a login shell, whereas RCs are executed every time a shell is created, login or non-login
RCs are for running commands, setting aliases, defining functions and other settings that cannot be exported to sub-shells.

Supplied MYVAR are marked for automatic export to the environment of subsequently executed commands.

export MYVAR
alias
unalias
function () {...}
set
unset

Bash

chmod +x script.sh

$VARIABLENAME vs. ${VARIABLENAME}
      $FIRST_$LAST   = $FIRST_ + $LAST
      ${FIRST}_$LAST = $FIRST +_ + $LAST
`CMD` == $(CMD)
$[<ARITHEMTIC EXPRESSION>]
FOR <VARIABLE> in <LIST>; do
      <COMMAND>
...
      <COMMAND> referencing <VARIABLE>
DONE

Example:

cat file
    peter
    john
vim script.sh

#!/bin/bash
file=$(cat $1)
for i in $file; do
    echo $i
done

Troubleshooting:

bash -x <SCRIPT> or 'set -x' ... 'set +x'
bash -v <SCRIPT> or 'set -v' ... 'set +v'

$0 = script name itself
$1 = first argument of the script
$, $@* = all arguments
$# = number of arguments
$? = exit status/code (exit 0 -> exit 255)

Comparison:

[ "$A" -eq "$B" ]; ... $?

'eq' or '=' = equal
'ne' or '!=' = not equal
'gt' = greater than
'ge' = greater/equal than
'lt' = less than
'le' = less/equal than
'z' = string is null
'n' = string is not null
'b' = file exists & block special
'c' = file exists & character special
'd' = is directory
'e' = exists
'f' = is regular file
'L' = is symbolic link
'r' = read permission granted
's' = non-zero size
'w' = write permission granted
'x' = execute permission granted
'ef' = same device & inode
'nt' = newer modification date
'ot' = older modification date
&& = AND
|| = OR

if <CONDITION>; then
      <CMD>
elif <STATEMENT>
else <STATEMENT>
fi

case <VALUE> in
      <PATTERN1>) <STATEMENT>;;
      <PATTERN2>) <STATEMENT>;;
      <PATTERN3>) <STATEMENT>;;
      <*>) ;;
esac

Exercises

dbbackup

vim dbbackup
chmod +x dbbbackup

#!/bin/bash
#RHCE page 341, guided exercise

#Variables
DBUSER=root
FMTOPTIONS='--skip-column-names -E'
COMMAND='SHOW DATABASES'
BACKUPDIR=/dbbackup

#Backup non-system databases
for DBNAME in $(mysql $FMOPTIONS -u $DBUSER -e "$COMMAND" | grep -v ^* | grep -v information_schema | grep -v performance_schema); do
    echo "Backing up \"$DBNAME\""
    mysqldump -u $DBUSER $DBNAME > $BACKUPDIR/$DBNAME.dump
done

#Add up size of all database dumps
for DBDUMP in $BACKUPDIR/*; do
    SIZE=$(stat --printf "%s\n" $DBDUMP)
    TOTAL=$[ $TOTAL + $SIZE]
done

#Report name, size, and percentage of total for each database dump
echo
for DBDUMP in $BACKUPDIR/*; do
    SIZE=$(stat --print "%s\n" $DBDUMP)
    echo "$DBDUMP,$SIZE,$[ 100 * $SIZE / $TOTAL ]%"
done

mkaccounts.orig

vim mkaccounts.orig
chmod +x mkaccounts.orig

#!/bin/bash
#RHCE page 347, lab exercise

#Variables
NEWUSERSFILE=/tmp/support/newusers

#Loop
for ENTRY in $(cat $NEWUSERSFILE); do
    #Extract first, last and tier fields
    FIRSTNAME=$(echo $ENTRY | cut -d: -f1)
    LASTNAME=$(echo $ENTRY | cut -d: -f2)
    TIER=$(echo $ENTRY | cut -d: -f4)
    #Make account name
    FIRSTINITIAL=$(echo $FIRSTNAME | cut -c 1 | tr 'A-Z' 'a-z')
    LOWERLASTNAME=$(echo $LASTNAME | tr 'A-Z' 'a-z')
    ACCTNAME=$$FIRSTINITIAL$LOWERLASTNAME
    #Create account
    useradd $ACCTNAME -c "$FIRSTNAME $LASTNAME"
done
TOTAL=$(cat $NEWUSERSFILE | wc -l)
TIER1COUNT=$(grep -c :1$ $NEWUSERSFILE)
TIER2COUNT=$(grep -c :2$ $NEWUSERSFILE)
TIER3COUNT=$(grep -c :3$ $NEWUSERSFILE)
TIER1PCT=$[ $TIER1COUNT * 100 / $TOTAL ]
TIER2PCT=$[ $TIER2COUNT * 100 / $TOTAL ]
TIER3PCT=$[ $TIER3COUNT * 100 / $TOTAL ]

#Print the report
echo "\"Tier 1\",\"$TIER1COUNT\",\"$TIER1PCT%\""
echo "\"Tier 2\",\"$TIER2COUNT\",\"$TIER2PCT%\""
echo "\"Tier 3\",\"$TIER3COUNT\",\"$TIER3PCT%\""

mkvhost

vim mkvhost
chmod +x mkvhost

#!/bin/bash
#RHCE page 363, guided exercise

#Variables
VHOSTNAME=$1
TIER=$2
HTTPDCONF=/etc/httpd/conf/httpd.conf
VHOSTCONFDIR=/etc/httpd/conf.vhost.d
DEFHOSTCONFFILE=$VHOSTCONFDIR/00-default-vhost.conf
VHOSTCONFFILE=$VHOSTCONFDIR/$VHOSTNAME.conf
WWWROOT=/srv
DEFVHOSTDOCROOT=$WWWROOT/default/www
VHOSTDOCROOT=$WWWROOT/$VHOSTNAME/www

#Check arguments
if [ "$VHOSTNAME" = '' ] || [ "$TIER" = '' ]; then
    echo "Usage: $0 VHOSTNAME TIER"
    exit 1
else

#Set support email address
   case $TIER in
    1)VHOSTADMIN='[email protected]'
      ;;
    2)VHOSTADMIN='[email protected]'
      ;;
    3)VHOSTADMIN='[email protected]'
      ;;
    *)echo "Invalid tier specified."
      exit 1
      ;;
   esac
fi

#Create conf directory one time if non-existent
if [ ! -d $VHOSTCONFDIR ]; then
    mkdir $VHOSTCONFDIR
    if [ $? -ne 0 ]; then
        echo "ERROR: Failed creating $VHOSTCONFDIR."
        exit 1
    fi
fi

#Add include one time if missing
grep -q '^IncludeOptional conf\.vhosts\.d/\*\.conf$' $HTTPDCONF
if [ $? -ne 0 ]; then
    #Backup before modifying
    cp -a $HTTPDCONF $HTTPDCONF.orig
    echo "IncludeOptional conf.vhosts.d/*.conf" >> $HTTPDCONF
    if [ $? -ne 0 ]; then
        echo "ERROR: Failed adding include directive."
        exit 1
    fi
fi

#Check for default virtual host
if [ ! -f $DEFVHOSTCONFFILE ]; then
    cat <<DEFCONFEOF > $DEFVHOSTCONFFILE
<VirtualHost _default_:80>
    DocumentRoot $DEFVHOSTDOCROOT
    CustomLog "logs/default-vhost.log" combined
</VirtualHost>
<Directory $DEFVHOSTDOCROOT>
    Require all granted
</Directory>
DEFCONFEOF
fi

if [ ! -d $DEFVHOSTDOCROOT ]; then
    mkdir -p $DEFVHOSTDOCROOT
    restorecon -Rv /srv/
fi

#Check for virtual host conflict
if [ -f $VHOSTCONFFILE ]; then
    echo "ERROR: $VHOSTCONFFILE already exists."
    exit 1
elif [ -d $VHOSTDOCROOT ]; then
    echo "ERROR: $VHOSTDOCROOT already exists."
    exit 1
else
    cat <<CONFEOF > $VHOSTCONFFILE
<Directory $VHOSTDOCROOT>
    Require all granted
    AllowOverride None
</Directory>
<VirtualHost *:80>
    DocumentRoot $VHOSTDOCROOT
    ServerName $VHOSTNAME
    ServerAdmin $VHOSTADMIN
    ErrorLog "logs/${VHOSTNAME}_error_log"
    CustomLog "logs/${VHOSTNAME}_access_log" common
</VirtualHost>
CONFEOF
    mkdir -p $VHOSTDOCROOT
    restorecon -Rv $WWWROOT
fi

#Check config and reload
apachectl configtest &> /dev/null
if [ $? -eq 0 ]; then
    systemctl reload httpd &> /dev/null
else
    echo "ERROR: Config error."
    exit 1
fi

mkaccounts

vi mkaccounts
chmod +x mkaccounts

#!/bin/bash
#RHCE page 370, lab exercise

#Variables
OPTION=$1
NEWUSERSFILE=/tmp/support/newusers

case $OPTION in
    '')
        ;;
    -v) VERBOSE=y
        ;;
    -h) echo "Usage: $0 [-h|-v]"
        echo
        exit
        ;;
     *) echo "Usage: $0 [-h|-v]"
        echo
        exit 1
        ;;
esac

#Test for dups and conflicts
ACCTEXIST=''
ACCTEXISTNAME=''
if [ $? -eq 0 ]; then
    ACCTEXIST=y
    ACCTEXISTNAME="$(grep ^$ACCTNAME: /etc/passwd | cut -f5 -d:)"
fi
if [ "$ACCTEXIST" = 'y' ] && [ "$ACCTEXISTNAME" = "$FIRSTNAME $LASTNAME" ]; then
    echo "Skipping $ACCTNAME. Duplicate found."
elif ["$ACCTEXIST" = 'y' ]; then
    echo "Skipping $ACCTNAME. Conflict found."
else useradd $ACCTNAME -c "$FIRSTNAME $LASTNAME"
    if [ "$VERBOSE" = 'y' ]; then
    echo "Added $ACCTNAME."
    fi
fi
#Loop
for ENTRY in $(cat $NEWUSERSFILE); do
    #Extract first, last and tier fields
    FIRSTNAME=$(echo $ENTRY | cut -d: -f1)
    LASTNAME=$(echo $ENTRY | cut -d: -f2)
    TIER=$(echo $ENTRY | cut -d: -f4)
    #Make account name
    FIRSTINITIAL=$(echo $FIRSTNAME | cut -c 1 | tr 'A-Z' 'a-z')
    LOWERLASTNAME=$(echo $LASTNAME | tr 'A-Z' 'a-z')
    ACCTNAME=$$FIRSTINITIAL$LOWERLASTNAME
    #Create account
    useradd $ACCTNAME -c "$FIRSTNAME $LASTNAME"
done
TOTAL=$(cat $NEWUSERSFILE | wc -l)
TIER1COUNT=$(grep -c :1$ $NEWUSERSFILE)
TIER2COUNT=$(grep -c :2$ $NEWUSERSFILE)
TIER3COUNT=$(grep -c :3$ $NEWUSERSFILE)
TIER1PCT=$[ $TIER1COUNT * 100 / $TOTAL ]
TIER2PCT=$[ $TIER2COUNT * 100 / $TOTAL ]
TIER3PCT=$[ $TIER3COUNT * 100 / $TOTAL ]

#Print the report
echo "\"Tier 1\",\"$TIER1COUNT\",\"$TIER1PCT%\""
echo "\"Tier 2\",\"$TIER2COUNT\",\"$TIER2PCT%\""
echo "\"Tier 3\",\"$TIER3COUNT\",\"$TIER3PCT%\""

myusers

vi myusers
chmod +x myusers

#!/bin/bash
#RHCE page 419, comprehensive review lab

if [ $# -eq 0 ]; then
    echo "$(basename $0) userlist"
    echo "$(basename $0) userinfo <USERNAME>"
fi

case $1 in
    userlist) grep -v ':/sbin/nologin$' /etc/passwd | cut -d: -f1 | sort
              ;;
    userinfo) if [ "$2" == "" ]; then
            echo "Please specify a username"
            exit 132
          fi
          if ! getent passwd $2 &> /dev/null; then
            echo "Invalid user"
            exit
          fi
          getent passwd $2 | cut -d: -f7
          ;;
    *) exit
       ;;
esac

Name		Name	Last commit message	Last commit date
Latest commit History 89 Commits
RHCE.jpg		RHCE.jpg
Readme.md		Readme.md
Readme.pdf		Readme.pdf
applicationwsgi.py		applicationwsgi.py
dbbackup		dbbackup
mkaccounts		mkaccounts
mkaccounts.orig		mkaccounts.orig
mkvhost		mkvhost
myusers		myusers
newusers		newusers

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RHCE 7 Summary

Repositories and Host Allowance/Denial

yum Commands

1. Allow SSH for a domain and deny SSH to all the others

2. Allow SSH for specific IP and block all the others

3. Denies all services to all hosts unless permitted in hosts.allow

4. Access granted by default, redundant file hosts.allow

5. Rules can be also in one file, for example

Recover root password

Temporarily Store passphrase

SERVICES

IPV4

Add Route

IPV6

TEAMING

BRIDGING

FIREWALL

Understand Zones

Rules

Example

Logging

Port Forwarding (Rich rule & Normal Rule)

SELinux

DNS

Installation

Configuration

NTP

Chrony

POSTFIX AS NULL CLIENT

Postconf Configuration

Gmail Specific Settings

iSCSI

Targets - server creating

Authentication

Targets - client accessing

Targets - client disconnecting

Reboot Server when iSCSI

Install a Kerberos Server

Install a Kerberos Client

Produce and Deliver Reports on System Load (Processor, Memory, Disk, and Network)

dstat

sysstat

Generate Reports with Sysstat

NFS

Server - Insecure

no_root_squash

Client - Insecure

Server - Secure

Client - Secure

Important

SELinux for NFS

Booleans

Provide NFS network shares to specific clients

NFS Server Configuration

NFS Client Configuration

Kerberos NFS Server Configuration

Kerberos NFS Client Configuration

SMB

Server

Another Example

Test Samba Connectivity on Server

Client - Single User

Client - Multiuser

SELinux for SMB

Context

Boolean

MARIADB

Managing Users and Access Rights

Backup - Logical

Backup - Physical

Restore - Logical

Restore - Physical

Queries

APACHE

New DocumentRoot for group 'webmasters'

Packages