How To: 2 Methods To Change TimeZone in Linux

proper timezone. How do I change the timezone on my Linux distribution. I use CentOS (Red Hat Linux). But, can you please explain me how to do this on all Linux distributions with some clear examples.

Answer: Use one of the following methods to change the timezone on your Linux system. One of these methods should work for you depending on the Linux distribution you are using.

Method 1: Change TimeZone Using /etc/localtime File

For this example, assume that your current timezone is UTC as shown below. You would like to change this to Pacific Time.

# date
Mon Sep 17 22:59:24 UTC 2010

On some distributions (for example, CentOS), the timezone is controlled by /etc/localtime file.

Delete the current localtime file under /etc/ directory

# cd /etc
# rm localtime

All US timezones are located under under the /usr/share/zoneinfo/US directory as shown below.

# ls /usr/share/zoneinfo/US/
Alaska          Arizona         Eastern         Hawaii          Michigan        Pacific
Aleutian        Central         East-Indiana    Indiana-Starke  Mountain        Samoa

Note: For other country timezones, browse the /usr/share/zoneinfo directory

Link the Pacific file from the above US directory to the /etc/localtime directory as shown below.

# cd /etc
# ln -s /usr/share/zoneinfo/US/Pacific localtime

Now the timezone on your Linux system is changed to US Pacific time as shown below.

# date
Mon Sep 17 23:10:14 PDT 2010

Method 2: Change TimeZone Using /etc/timezone File

On some distributions (for example, Ubuntu), the timezone is controlled by /etc/timezone file.

For example, your current timezone might be US Eastern time (New York) as shown below.

# cat /etc/timezone
America/New_York

To change this to US Pacific time (Los Angeles), modify the /etc/timezone file as shown below.

# vim /etc/timezone
America/Los_Angeles

Also, set the timezone from the command line using the TZ variable.

# export TZ=America/Los_Angeles

Linux Beginners Guide to NFS Mount Using Exportfs

Using NFS (Network File System), you can mount a disk partition of a remote machine as if it is a local disk. This article explains how to export a file system to a remote machine and mount it both temporarily and permanently.

1. Export File System to Remote Server using exportfs

To export a directory to a remote machine, do the following.

exportfs REMOTEIP:PATH

• REMOTEIP – IP of the remote server to which you want to export.
• : – delimiter
• PATH – Path of directory that you want to export.

2. Mount Remote Server File System as a Local Storage

To mount the remote file system on the local server, do the following.

mount REMOTEIP:PATH PATH

Explanation

• REMOTEIP – IP of the remote server which exported the file system
• : – delimeter
• PATH – Path of directory which you want to export.

3. Unmount Remote File System

Umount the remote file system mounted on the local server using the normal umount PATH. For more option refer to umount command examples.

4. Unexport the File System

You can check the exported file system as shown below.

# exportfs
/publicdata webserver.pq.net

To unexport the file system, use the -u option as shown below.

# exportfs -u REMOTEIP:PATH

After unexporting, check to make sure it is not available for NFS mount as shown below.

# exportfs

5. Make NFS Export Permanent Across System Reboot

Export can be made permanent by adding that entry into /etc/exports file.

# cat /etc/exports
/publicdata  webserver.pq.net

6. Make the Mount Permanent Across Reboot

mount can be made permanent by adding that entry into /etc/fstab file.

# cat /etc/fstab
webserver.pq.net:/publicdata    /mydata   ext3    defaults   0 0

9 Linux ethtool Examples to Manipulate Ethernet Card (NIC Card)

utility is used to view and change the ethernet device parameters.

1. List Ethernet Device Properties

When you execute ethtool command with a device name, it displays the following information about the ethernet device.

# ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Advertised auto-negotiation: Yes
        Speed: 100Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: d
        Wake-on: d
        Link detected: yes

This above ethtool output displays ethernet card properties such as speed, wake on, duplex and the link detection status. Following are the three types of duplexes available.

• Full duplex : Enables sending and receiving of packets at the same time. This mode is used when the ethernet device is connected to a switch.
• Half duplex : Enables either sending or receiving of packets at a single point of time. This mode is used when the ethernet device is connected to a hub.
• Auto-negotiation : If enabled, the ethernet device itself decides whether to use either full duplex or half duplex based on the network the ethernet device attached to.

2. Change NIC Parameter Using ethtool Option -s autoneg

The above ethtool eth0 output displays that the “Auto-negotiation” parameter is in enabled state. You can disable this using autoneg option in the ethtool as shown below.

# ifdown eth0
    eth0      device: Broadcom Corporation NetXtreme II BCM5709 Gigabit Ethernet (rev 20)
    eth0      configuration: eth-bus-pci-0000:0b:00.0

# ethtool  -s eth0 autoneg off

# ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  Not reported
        Advertised auto-negotiation: No
        Speed: Unknown! (65535)
        Duplex: Unknown! (255)
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: off
        Supports Wake-on: g
        Wake-on: g
        Link detected: no
# ifup eth0

After the above change, you could see that the “link detection” value changed to down and auto-negotiation is in off state.

3. Change the Speed of Ethernet Device

Using ethtool you can change the speed of the ethernet device to work with the certain network devices, and the newly assign speed value should be within the limited capacity.

# ethtool -s eth0 speed 100 autoneg off

# ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  Not reported
        Advertised auto-negotiation: No
        Speed: Unknown! (65535)
        Duplex: Unknown! (255)
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: off
        Supports Wake-on: g
        Wake-on: g
        Link detected: no

Once you change the speed when the adapter is online, it automatically goes offline, and you need to bring it back online using ifup command.

# ifup eth0
    eth0      device: Broadcom Corporation NetXtreme II BCM5709 Gigabit Ethernet (rev 20)
    eth0      configuration: eth-bus-pci-0000:0b:00.0
Checking for network time protocol daemon (NTPD):                     running

# ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  Not reported
        Advertised auto-negotiation: No
        Speed: 100Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: off
        Supports Wake-on: g
        Wake-on: g
        Link detected: yes

As shown in the above output, the speed changed from 1000Mb/s to 100Mb/s and auto-negotiation parameter is unset.

To change the Maximum Transmission Unit (MTU), refer to our ifconfig examples article.

4. Display Ethernet Driver Settings

ethtool -i option displays driver version, firmware version and bus details as shown below.

# ethtool -i eth0
driver: bnx2
version: 2.0.1-suse
firmware-version: 1.9.3
bus-info: 0000:04:00.0

5. Display Auto-negotiation, RX and TX of eth0

View the autonegotiation details about the specific ethernet device as shown below.

# ethtool -a eth0
Pause parameters for eth0:
Autonegotiate:  on
RX:             on
TX:             on

6. Display Network Statistics of Specific Ethernet Device

Use ethtool -S option to display the bytes transfered, received, errors, etc, as shown below.

# ethtool -S eth0
NIC statistics:
     rx_bytes: 74356477841
     rx_error_bytes: 0
     tx_bytes: 110725861146
     tx_error_bytes: 0
     rx_ucast_packets: 104169941
     rx_mcast_packets: 138831
     rx_bcast_packets: 59543904
     tx_ucast_packets: 118118510
     tx_mcast_packets: 10137453
     tx_bcast_packets: 2221841
     tx_mac_errors: 0
     tx_carrier_errors: 0
     rx_crc_errors: 0
     rx_align_errors: 0
     tx_single_collisions: 0
     tx_multi_collisions: 0
     tx_deferred: 0
     tx_excess_collisions: 0
     tx_late_collisions: 0
     tx_total_collisions: 0
     rx_fragments: 0
     rx_jabbers: 0
     rx_undersize_packets: 0
     rx_oversize_packets: 0
     rx_64_byte_packets: 61154057
     rx_65_to_127_byte_packets: 55038726
     rx_128_to_255_byte_packets: 426962
     rx_256_to_511_byte_packets: 3573763
     rx_512_to_1023_byte_packets: 893173
     rx_1024_to_1522_byte_packets: 42765995
     rx_1523_to_9022_byte_packets: 0
     tx_64_byte_packets: 3633165
     tx_65_to_127_byte_packets: 51169838
     tx_128_to_255_byte_packets: 3812067
     tx_256_to_511_byte_packets: 113766
     tx_512_to_1023_byte_packets: 104081
     tx_1024_to_1522_byte_packets: 71644887
     tx_1523_to_9022_byte_packets: 0
     rx_xon_frames: 0
     rx_xoff_frames: 0
     tx_xon_frames: 0
     tx_xoff_frames: 0
     rx_mac_ctrl_frames: 0
     rx_filtered_packets: 14596600
     rx_discards: 0
     rx_fw_discards: 0

7. Troubleshoot the Ethernet Connection Issues

When there is a problem with the network connection, you might want to check (or change) the ethernet device parameters explained in the above examples, when you see following issues in the output of ethtool command.

• Speed and Duplex value is shown as Unknown
• Link detection value is shown as No

Upon successful connection, the three parameters mentioned above gets appropriate values. i.e Speed is assigned with known value, Duplex become either Full/Half, and the Link detection becomes Yes.

After the above changes, if the Link Detection still says “No”, check whether there are any issues in the cables that runs from the switch and the system, you might want to dig into that aspect further.

To capture and analyze packets from a specific network interface, use tcpdump utility.

8. Identify Specific Device From Multiple Devices (Blink LED Port of NIC Card)

Let us assume that you have a machine with four ethernet adapters, and you want to identify the physical port of a particular ethernet card. (For example, eth0).

Use ethtool option -p, which will make the corresponding LED of physical port to blink.

# ethtool -p eth0

9. Make Changes Permanent After Reboot

If you’ve changed any ethernet device parameters using the ethtool, it will all disappear after the next reboot, unless you do the following.

On ubuntu, you have to modify /etc/network/interfaces file and add all your changes as shown below.

# vim /etc/network/interfaces
post-up ethtool -s eth2 speed 1000 duplex full autoneg off

The above line should be the last line of the file. This will change speed, duplex and autoneg of eth2 device permanently.

On SUSE, modify the /etc/sysconfig/network/ifcfg-eth-id file and include a new script using POST_UP_SCRIPT variable as shown below. Include the below line as the last line in the corresponding eth1 adpater config file.

# vim /etc/sysconfig/network/ifcfg-eth-id
POST_UP_SCRIPT='eth1'

Then, create a new file scripts/eth1 as shown below under /etc/sysconfig/network directory. Make sure that the script has execute permission and ensure that the ethtool utility is present under /sbin directory.

# cd /etc/sysconfig/network/

# vim scripts/eth1
#!/bin/bash
/sbin/ethtool -s duplex full speed 100 autoneg off

Linux modprobe Command Examples to View, Install, Remove Modules

modprobe utility is used to add loadable modules to the Linux kernel. You can also view and remove modules using modprobe command.

Linux maintains /lib/modules/$(uname-r) directory for modules and its configuration files (except /etc/modprobe.conf and /etc/modprobe.d).

In Linux kernel 2.6, the .ko modules are used instead of .o files since that has additional information that the kernel uses to load the modules. The example in this article are done with using modprobe on Ubuntu.

1. List Available Kernel Modules

modprobe -l will display all available modules as shown below.

$ modprobe -l | less
kernel/arch/x86/kernel/cpu/mcheck/mce-inject.ko
kernel/arch/x86/kernel/cpu/cpufreq/e_powersaver.ko
kernel/arch/x86/kernel/cpu/cpufreq/p4-clockmod.ko
kernel/arch/x86/kernel/msr.ko
kernel/arch/x86/kernel/cpuid.ko
kernel/arch/x86/kernel/apm.ko
kernel/arch/x86/kernel/scx200.ko
kernel/arch/x86/kernel/microcode.ko
kernel/arch/x86/crypto/aes-i586.ko
kernel/arch/x86/crypto/twofish-i586.ko

2. List Currently Loaded Modules

While the above modprobe command shows all available modules, lsmod command will display all modules that are currently loaded in the Linux kernel.

$ lsmod | less
soundcore          7264   1 snd
ppdev                6688   0
snd_page_alloc   9156    1 snd_pcm
psmouse            56180  0
lp                     8964    0

3. Install New modules into Linux Kernel

In order to insert a new module into the kernel, execute the modprobe command with the module name.

Following example loads vmhgfs module to Linux kernel on Ubuntu.

$ sudo modprobe vmhgfs

Once a module is loaded, verify it using lsmod command as shown below.

$ lsmod | grep vmhgfs
vmhgfs                 50772  0

The module files are with .ko extension. If you like to know the full file location of a specific Linux kernel module, use modprobe command and do a grep of the module name as shown below.

$ modprobe | grep vmhgfs
misc/vmhgfs.ko

$ cd /lib/modules/2.6.31-14-generic/misc

$ ls vmhgfs*
vmhgfs.ko

Note: You can also use insmod for installing new modules into the Linux kernel.

4. Load New Modules with the Different Name to Avoid Conflicts

Consider, in some cases you are supposed to load a new module but with the same module name another module got already loaded for different purposes.

If for some strange reasons, the module name you are trying to load into the kernel is getting used (with the same name) by a different module, then you can load the new module using a different name.

To load a module with a different name, use the modprobe option -o as shown below.

$ sudo modprobe vmhgfs -o vm_hgfs

$ lsmod  | grep vm_hgfs
vm_hgfs                   50772  0

5. Remove the Currently Loaded Module

If you’ve loaded a module to Linux kernel for some testing purpose, you might want to unload (remove) it from the kernel.

Use modprobe -r option to unload a module from the kernel as shown below.

modprobe -r vmhgfs

How To Manage Packages Using apt-get, apt-cache, apt-file and dpkg Commands ( With 13 Practical Examples )

based systems (including Ubuntu) uses apt-* commands for managing packages from the command line.

In this article, using Apache 2 installation as an example, let us review how to use apt-* commands to view, install, remove, or upgrade packages.

1. apt-cache search: Search Repository Using Package Name

If you are installing Apache 2, you may guess that the package name is apache2.  To verify whether it is a valid package name, you may want to search the repository for that particular package name as shown below.

The following example shows how to search the repository for a specific package name.

$ apt-cache search ^apache2$
apache2 - Apache HTTP Server metapackage

2. apt-cache search: Search Repository Using Package Description

If you don’t know the exact name of the package, you can still search using the package description as shown below.

$ apt-cache search "Apache HTTP Server"
apache2 - Apache HTTP Server metapackage
apache2-doc - Apache HTTP Server documentation
apache2-mpm-event - Apache HTTP Server - event driven model
apache2-mpm-prefork - Apache HTTP Server - traditional non-threaded model
apache2-mpm-worker - Apache HTTP Server - high speed threaded model
apache2.2-common - Apache HTTP Server common files

3. apt-file search: Search Repository Using a Filename from the Package

Sometimes you may know the configuration file name (or) the executable name from the package that you would like to install.

The following example shows that apache2.conf file is part of the apache2.2-common package. Search the repository with a configuration file name using apt-file command as shown below.

$ apt-file search apache2.conf
apache2.2-common: /etc/apache2/apache2.conf
apache2.2-common: /usr/share/doc/apache2.2-common/examples/apache2/apache2.conf.gz

4. apt-cache show: Basic Information About a Package

Following example displays basic information about apache2 package.

$ apt-cache show apache2
Package: apache2
Priority: optional
Maintainer: Ubuntu Core Developers
Original-Maintainer: Debian Apache Maintainers
Version: 2.2.11-2ubuntu2.3
Depends: apache2-mpm-worker (>= 2.2.11-2ubuntu2.3)
 | apache2-mpm-prefork (>= 2.2.11-2ubuntu2.3)
 | apache2-mpm-event (>= 2.2.11-2ubuntu2.3)
Filename: pool/main/a/apache2/apache2_2.2.11-2ubuntu2.3_all.deb
Size: 46350
Description: Apache HTTP Server metapackage
 The Apache Software Foundation's goal is to build a secure, efficient and
 extensible HTTP server as standards-compliant open source software.
Homepage: http://httpd.apache.org/

5. apt-cache showpkg: Detailed Information About a Package

“apt-cache show” displays basic information about a package. Use “apt-cache showpkg” to display detailed information about a package as shown below.

$ apt-cache showpkg apache2
Package: apache2
Versions:
2.2.11-2ubuntu2.3 (/var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_jaunty-updates_main_binary-i386_Packages) (/var/lib/apt/lists/security.ubuntu.com_ubuntu_dists_jaunty-security_main_binary-i386_Packages)
 Description Language:
                 File: /var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_jaunty-updates_main_binary-i386_Packages
                  MD5: d24f049cd70ccfc178dd8974e4b1ed01
Reverse Depends:
  squirrelmail,apache2
  squid3-cgi,apache2
  phpmyadmin,apache2
  mahara-apache2,apache2
  ipplan,apache2
Dependencies:
  2.2.11-2ubuntu2.3 - apache2-mpm-worker (18 2.2.11-2ubuntu2.3) apache2-mpm-prefork (18 2.2.11-2ubuntu2.3) apache2-mpm-event (2 2.2.11-2ubuntu2.3)
  2.2.11-2ubuntu2 - apache2-mpm-worker (18 2.2.11-2ubuntu2) apache2-mpm-prefork (18 2.2.11-2ubuntu2) apache2-mpm-event (2 2.2.11-2ubuntu2)
Provides:
  2.2.11-2ubuntu2.3 -
  2.2.11-2ubuntu2 -
Reverse Provides:
  apache2-mpm-itk 2.2.6-02-1build4.3
  apache2-mpm-worker 2.2.11-2ubuntu2.3
  apache2-mpm-prefork 2.2.11-2ubuntu2.3
  apache2-mpm-prefork 2.2.11-2ubuntu2
  apache2-mpm-event 2.2.11-2ubuntu2

6. apt-file list: List all the Files Located Inside a Package

Use “apt-file list” to display all the files located inside the apache2 package as shown below.

$ apt-file list apache2 | more
apache2: /usr/share/bug/apache2/control
apache2: /usr/share/bug/apache2/script
apache2: /usr/share/doc/apache2/NEWS.Debian.gz
apache2: /usr/share/doc/apache2/README.Debian.gz
apache2: /usr/share/doc/apache2/changelog.Debian.gz
...

7. apt-cache depends: List all Dependent Packages

Before installation, if you like to view all the dependent packages, use “apt-cache depends” as shown below.

$ apt-cache depends apache2
apache2
 |Depends: apache2-mpm-worker
 |Depends: apache2-mpm-prefork
  Depends: apache2-mpm-event

8. dpkg -l: Is the Package Already Installed?

Before installing a package, you may want to make sure it is not already installed as shown below using dpkg -l command.

$ dpkg -l | grep -i apache

9. apt-get install: Install a Package

Finally, install the package using “apt-get install” as shown below.

$ sudo apt-get install apache2
[sudo] password for ramesh: 

The following NEW packages will be installed:
  apache2 apache2-mpm-worker apache2-utils apache2.2-common libapr1
  libaprutil1 libpq5

0 upgraded, 7 newly installed, 0 to remove and 26 not upgraded.

10. dpkg -l : Verify Whether the Package got Successfully Installed

After installing the package, use “dpkg -l” to make sure it got installed successfully.

$ dpkg -l | grep apache
ii  apache2             2.2.11-2ubuntu2.3  Apache HTTP Server metapackage
ii  apache2-mpm-worker  2.2.11-2ubuntu2.3  Apache HTTP Server - high speed threaded mod
ii  apache2-utils       2.2.11-2ubuntu2.3  utility programs for webservers
ii  apache2.2-common    2.2.11-2ubuntu2.3  Apache HTTP Server common files

11. apt-get remove: Delete a Package

Use “apt-get purge” or “apt-get remove” to delete a package as shown below.

$ sudo apt-get purge apache2

(or)

$ sudo apt-get remove apache2

The following packages were automatically installed and are no longer required:
  apache2-utils linux-headers-2.6.28-11 libapr1 apache2.2-common
  linux-headers-2.6.28-11-generic apache2-mpm-worker libpq5 libaprutil1

Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  apache2
0 upgraded, 0 newly installed, 1 to remove and 26 not upgraded.
Removing apache2 ...

• apt-get remove will not delete the configuration files of the package
• apt-get purge will delete the configuration files of the package

12. apt-get -u install: Upgrade a Specific Package

The following example shows how to upgrade one specific package.

$ sudo apt-get -u install apache2
Reading package lists... Done
Building dependency tree
Reading state information... Done
apache2 is already the newest version.
The following packages were automatically installed and are no longer required:
  linux-headers-2.6.28-11 linux-headers-2.6.28-11-generic
Use 'apt-get autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 26 not upgraded.

13. apt-get -u upgrade: Upgrade all Packages

To upgrade all the packages to it’s latest version, use “apt-get -u upgrade” as shown below.

$ sudo apt-get -u upgrade
The following packages will be upgraded:
  libglib2.0-0 libglib2.0-data libicu38 libsmbclient libwbclient0
  openoffice.org-base-core openoffice.org-calc openoffice.org-common
  openoffice.org-core openoffice.org-draw openoffice.org-emailmerge
  openoffice.org-gnome openoffice.org-gtk openoffice.org-impress
  openoffice.org-math openoffice.org-style-human openoffice.org-writer
  python-uno samba-common smbclient ttf-opensymbol tzdata
26 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.