Linux How To Tips and Links

Install Centos Linux using Flash USB drive

  • Format the USB drive in Windows as Fat32, Quick format is OK
  • Transfer ISO content to USB thumb drive using UNetbootin
    • Download and launch UNetbootin
    • Select Diskimage and click the “. . .” button.
    • Find the ISO and click Open
    • Make sure Type is USB drive and the Drive letter is what your Windows detect.
    • Click OK
    • Your ISO content will be copied to USB thumb drive
  • Copy the ISO file that you used with UNetbootin to the root of the USB thumb drive, eg. the ISO file should be F:\CentOS-6.3-x86_64-bin-DVD1.iso

This does not work with Centos 6.4, the image is too big to fit into Fat32 filesystem.

Groups included in each option at install time

Based on /usr/lib/anaconda/installclasses/rhel.py from images/install.img the following options are available:

  • Desktop: base, core, debugging, directory-client, java-platform, network-file-system-client, server-platform, fonts, print-client, basic-desktop, desktop-debugging, desktop-platform, general-desktop, graphical-admin-tools, input-methods, legacy-x, x11, internet-applications, internet-browser, office-suite, remote-desktop-clients
  • Minimal Desktop: base, core, debugging, directory-client, java-platform, network-file-system-client, server-platform, fonts, print-client, basic-desktop, desktop-debugging, desktop-platform, input-methods, legacy-x, x11, internet-browser, remote-desktop-clients
  • Minimal: core
  • Basic Server: base, console-internet, core, debugging, directory-client, hardware-monitoring, java-platform, large-systems, network-file-system-client, performance, perl-runtime, server-platform
  • Database Server: base, console-internet, core, debugging, directory-client, hardware-monitoring, java-platform, large-systems, network-file-system-client, performance, perl-runtime, server-platform, mysql-client, mysql, postgresql-client, postgresql, system-admin-tools
  • Web Server: base, console-internet, core, debugging, directory-client, java-platform, network-file-system-client, performance, perl-runtime, server-platform, web-server, web-servlet, php, turbogears, mysql-client, postgresql-client
  • Virtual Host: base, console-internet, core, debugging, directory-client, hardware-monitoring, java-platform, large-systems, network-file-system-client, performance, perl-runtime, server-platform, virtualization, virtualization-client, virtualization-platform
  • Software Development Workstation: base, core, debugging, directory-client, java-platform, network-file-system-client, performance, perl-runtime, server-platform, fonts, print-client, basic-desktop, desktop-debugging, desktop-platform, general-desktop, graphical-admin-tools, input-methods, legacy-x, x11, internet-browser, graphics, emacs, tex, remote-desktop-clients, virtualization, virtualization-client, virtualization-platform, desktop-platform-devel, development, eclipse, server-platform-devel, technical-writing, additional-devel
  • The contents of each group can be seen by
    • yum groupinfo <groupname>

Configuring Centos networking

Interface Configuration

DHCP

[root@example ~]# vim /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
BOOTPROTO=dhcp
DHCP_HOSTNAME=servername
NM_CONTROLLED="no"
PERSISTENT_DHCLIENT=1
ONBOOT="yes"
TYPE=Ethernet
DEFROUTE=yes
PEERDNS=yes
PEERROUTES=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME="eth0"

Static

[username@hostname]$ vim /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
HWADDR="00:21:70:10:7E:CD"
NM_CONTROLLED="no"
ONBOOT="yes"
BOOTPROTO=static
# BOOTPROTO=dhcp
IPADDR=10.16.1.106
NETMASK=255.255.255.0
# The GATEWAY is sometimes in: /etc/sysconfig/network
GATEWAY=10.16.1.1
DNS1=10.1.1.2
DNS2=10.1.1.3
DOMAIN=test.com

DNS resolvers and search domain

vim /etc/resolv.conf
domain domain.com
search domain.com
nameserver 10.1.1.2
nameserver 10.1.1.3

Hostname and other options

[username@hostname]$ vim /etc/sysconfig/network
NETWORKING=yes
HOSTNAME=acme.example.com
DNS1=10.16.1.112
DNS2=8.8.8.8
## DNS2=76.242.0.28
SEARCH=example.com

Print the network node hostname

# uname -n
centos01.how2centos.com

Show the systems DNS domain name

# dnsdomainname
how2centos.com

Using a single command line to configure the network

# ifconfig eth0 192.168.0.10 netmask 255.255.255.0

or run System Config

# system-config-network

Midnight commander

Getting Midnight Commander line drawing to work with PuTTY

VNC

  • Start VNC server:
vncserver -geometry 1960x1080
  • kill vnc listener:
vncserver -kill :1
  • Change vnc password:
vncpasswd

Add GNOME to a CentOS Minimal Install

http://www.idevelopment.info/data/Unix/Linux/LINUX_AddGNOMEToCentOSMinimalInstall.shtml

  • Install Desktop Packages
    • #yum -y groupinstall “Desktop” “Desktop Platform” “X Window System” “Fonts”
  • You can also install the following optional GUI packages.
    • #yum -y groupinstall “Graphical Administration Tools”
    • #yum -y groupinstall “Internet Browser”
    • # yum -y groupinstall “General Purpose Desktop”
    • # yum -y groupinstall “Office Suite and Productivity”
    • # yum -y groupinstall “Graphics Creation Tools”
  • Enable GNOME. Since the server was previously running on CLI mode, we need to change the initialization process for the machine to boot up in GUI mode. Open /etc/inittab using a text editor and change following line:
    • id:3:initdefault: To:
    • id:5:initdefault:

Note that you can switch from GUI to CLI mode manually by using following method:

  GUI to CLI: Ctrl + Alt + F6
  CLI to GUI: Ctrl + Alt + F1

Using tar

Compressed Tar

GZip compressed TAR files are usually used to distribute files between users of Linux, BSD or UNIX. An idea what is possible with tar may be found under How to use your Tapedrive. More information is in the manpage of tar.

Some short Ideas how to create or extract a tar.gz:

tar cvfz archive.tar.gz directory
-> put the content of the directory directory into the file archive.tar.gz

tar tvfz archive.tar.gz
-> shows the content of the file archive.tar.gz

tar xvfz archive.tar.gz
-> extract archive.tar.gz

Asterix PBX

Asterisk homepage

main configuration file is in sip.conf extensions are in extensions.conf

Using the console: asterisk -rc

Commands:

sip debug
sip nodebug
reload -reloads the extensions after editing the config files
show dialplan - shows extensions
exit - exit console
stop now

asterisk -vvvc

Other

Linux guides

Determine Linux Version

  1. #cat /proc/version
  2. #cat /etc/redhat-release
  3. #uname -r

Password and user management

cat /etc/passwd  :pasword list
cat /etc/group   :list of groups
cat /etc/sudoers :list of sudo users
groupadd GroupName
/usr/sbin/useradd -c "First Last' -g GroupName UserName    :create username, add to group
passwd UserName  :change password
groups UserName  :list user groups
cat /etc/yp.conf :list user authentication binding  

Firewall

Uninstall packages

Querry for the name of what you want to unistall:

rpm -qa | grep -i 'mysql'

Uninstall using yum:

yum remove mysql-libs

DHCP dhcpd

Install dhcp

rpm -q chkconfig dhcp

Setup dhcp to start automatically using chkconfig:

chkconfig --list dhcpd
chkconfig dhcpd on

Configure NIS client

Configure yp: http://www.server-world.info/en/note?os=CentOS_6&p=nis&f=2

#vim /etc/sysconfig/network

NETWORKING=yes
HOSTNAME=localhostname
NISDOMAIN=domainname

#vim /etc/sysconfig/authconfig

USENIS=yes   (change from no)

#vim /etc/yp.conf

domain  domainname server 10.1.1.3

#vi /etc/nsswitch.conf

passwd:     files nis
shadow:     files nis
group:      files nis

#vi /etc/pam.d/system-auth (automatic home folder creation)

session     optional      pam_mkhomedir.so skel=/etc/skel umask=077

#vim /etc/pam.d/sshd (automatic home folder creation for ssh login)

session     optional      pam_mkhomedir.so skel=/etc/skel umask=077

#chkconfig rpcbind on

# chkconfig ypbind on

# shutdown -r now

Network Time (NTP)

NTP Client configuration

In order to keep the time accurate on a Linux system one can either:

  • Run the ntpd (network time protocol daemon) which will run all the time and continuously adjust the system time when clocks drift. or alternatively:
  • Call ntpdate periodically (e.g. from cron)

Q: What are the pros and cons of each of these two methods?

A: ntpdate is deprecated as of September 2012; apparently ntpd now has the ability to do one-time updates if needed, and ntpdate is based on "long-neglected" ntpd code. 

Q: Which different scenarios call for picking one over the other?

A: ntpd offers continuous adjustments and maintains better accuracy over time, which can be important for databases. But of course this would require slightly 
   more network traffic (presumably negligible for exchanging simple timestamps) as well as an always-online network connection, slight consumption of RAM and CPU, etc. 
   But all these downsides are tiny in a modern computing environment; overall I doubt there are good reasons to substitute cron for ntpd.
   You can also run ntpd using cron:
   # echo '30 * * * * root /usr/sbin/ntpd -q -u ntp:ntp' > /etc/cron.d/ntpd
   The above instructs crond to run ntpd and after setting the clock just exit, and the -u option instructs it to run as the ntp user.

Server configuration

Install the ntp package:

# yum install ntp

Edit config file and add servers

# vim /etc/ntp.conf

Servers:

server 0.centos.pool.ntp.org
server 1.centos.pool.ntp.org
server 2.centos.pool.ntp.org
#and/or:
server 0.north-america.pool.ntp.org
server 1.north-america.pool.ntp.org
server 2.north-america.pool.ntp.org
server 3.north-america.pool.ntp.org

Add your local network to allow access

# Hosts on local network are less restricted.
restrict 10.0.0.0 mask 255.0.0.0 nomodify notrap
restrict 192.168.0.0 mask 255.255.0.0 nomodify notrap

Add location for logs

logfile /var/log/ntp.log

Update your firewall settings, open /etc/sysconfig/iptables.

# vim /etc/sysconfig/iptables
Add the following line, before the final LOG and DROP lines for the RH-Firewall-1-INPUT chain:
 -I OUTPUT -p udp -m udp -m multiport --dports 123 -m state --state NEW -j ACCEPT
 -I INPUT -p udp -m udp -m multiport --dports 123 -m state --state NEW -j ACCEPT

Start ntpd

# service ntpd start
# service iptables restart

Install ntp service to start on reboot

#chkconfig ntpd on

Troubleshooting

Check that the service is listening on the port:

# netstat -tulpn |grep ntpd

Test the ntp:

# ntpstat
# ntpq -pn
# ntpq -p

Check the logs

#cat /var/log/ntp.log

If ntpd does not work (but is correctly configured) assuming an RFC-compliant implementation, your clock may have drifted too far. If you view /var/log/ntp.log, you may see an entry similar to: 18 Aug 21:04:40 ntpd[7220]: time correction of 1738 seconds exceeds sanity limit (1000); set clock manually to the correct UTC time.

This sanity check can be overridden by adding the command-line switch “-g” when starting ntpd. (For OpenBSD's NTP server OpenNTPD, use “-s”).

ntpd -g

To manually force the time to synchronize, use:

ntpd -q

Troubleshooting on client

On client execute this command:

# ntpdate -d xx.xx.xx.xx (your time server)

Check the output, if you see:

xx.xx.xx.xx: Server dropped: strata too high
stratum 16, precision -20, leap 11, trust 000

stratum 16 indicates that the time server is not synchronized, possibly unable to reach its time servers configured in /etc/ntp.conf

Install VM ware tools

yum -y install perl
mkdir /mnt/cdrom
mount /dev/cdrom /mnt/cdrom
cp /mnt/cdrom/VMwareTools-*.tar.gz /tmp
umount /mnt/cdrom
tar -zxf /tmp/VMwareTools-*.tar.gz -C /tmp
cd /
./tmp/vmware-tools-distrib/vmware-install.pl --default
rm -f /tmp/VMwareTools-*.tar.gz
rm -rf /tmp/vmware-tools-distrib
rm mysymlink ; ln -s mytargetfile mysymlink

or change the target of a soft link without deleting the old one by forcing ln to do so.

ln -s /home/Data1 /home/Stores/abc
ln -f -s /home/Data2 /home/Stores/abc

Asterisk to Altigen

howto/linuxhowto.txt · Last modified: 2015/04/16 16:26 (external edit)
CC Attribution-Noncommercial-Share Alike 4.0 International
www.chimeric.de Valid CSS Driven by DokuWiki do yourself a favour and use a real browser - get firefox!! Recent changes RSS feed Valid XHTML 1.0