sabato 20 ottobre 2012

How to Backup Linux? 15 rsync Command Examples

rsync stands for remote sync.
rsync is used to perform the backup operation in UNIX / Linux.
rsync utility is used to synchronize the files and directories from one location to another in an effective way. Backup location could be on local server or on remote server.

Important features of rsync

  • Speed: First time, rsync replicates the whole content between the source and destination directories. Next time, rsync transfers only the changed blocks or bytes to the destination location, which makes the transfer really fast.
  • Security: rsync allows encryption of data using ssh protocol during transfer.
  • Less Bandwidth: rsync uses compression and decompression of data block by block at the sending and receiving end respectively. So the bandwidth used by rsync will be always less compared to other file transfer protocols.
  • Privileges: No special privileges are required to install and execute rsync

Syntax

$ rsync options source destination
Source and destination could be either local or remote. In case of remote, specify the login name, remote server name and location.

Example 1. Synchronize Two Directories in a Local Server

To sync two directories in a local computer, use the following rsync -zvr command.
$ rsync -zvr /var/opt/installation/inventory/ /root/temp
building file list ... done
sva.xml
svB.xml
.
sent 26385 bytes  received 1098 bytes  54966.00 bytes/sec
total size is 44867  speedup is 1.63
$
In the above rsync example:
  • -z is to enable compression
  • -v verbose
  • -r indicates recursive
Now let us see the timestamp on one of the files that was copied from source to destination. As you see below, rsync didn’t preserve timestamps during sync.
$ ls -l /var/opt/installation/inventory/sva.xml /root/temp/sva.xml
-r--r--r-- 1 bin  bin  949 Jun 18  2009 /var/opt/installation/inventory/sva.xml
-r--r--r-- 1 root bin  949 Sep  2  2009 /root/temp/sva.xml

Example 2. Preserve timestamps during Sync using rsync -a

rsync option -a indicates archive mode. -a option does the following,
  • Recursive mode
  • Preserves symbolic links
  • Preserves permissions
  • Preserves timestamp
  • Preserves owner and group
Now, executing the same command provided in example 1 (But with the rsync option -a) as shown below:
$ rsync -azv /var/opt/installation/inventory/ /root/temp/
building file list ... done
./
sva.xml
svB.xml
.
sent 26499 bytes  received 1104 bytes  55206.00 bytes/sec
total size is 44867  speedup is 1.63
$
As you see below, rsync preserved timestamps during sync.
$ ls -l /var/opt/installation/inventory/sva.xml /root/temp/sva.xml
-r--r--r-- 1 root  bin  949 Jun 18  2009 /var/opt/installation/inventory/sva.xml
-r--r--r-- 1 root  bin  949 Jun 18  2009 /root/temp/sva.xml

Example 3. Synchronize Only One File

To copy only one file, specify the file name to rsync command, as shown below.
$ rsync -v /var/lib/rpm/Pubkeys /root/temp/
Pubkeys

sent 42 bytes  received 12380 bytes  3549.14 bytes/sec
total size is 12288  speedup is 0.99

Example 4. Synchronize Files From Local to Remote

rsync allows you to synchronize files/directories between the local and remote system.
$ rsync -avz /root/temp/ thegeekstuff@192.168.200.10:/home/thegeekstuff/temp/
Password:
building file list ... done
./
rpm/
rpm/Basenames
rpm/Conflictname

sent 15810261 bytes  received 412 bytes  2432411.23 bytes/sec
total size is 45305958  speedup is 2.87
While doing synchronization with the remote server, you need to specify username and ip-address of the remote server. You should also specify the destination directory on the remote server. The format is username@machinename:path
As you see above, it asks for password while doing rsync from local to remote server.
Sometimes you don’t want to enter the password while backing up files from local to remote server. For example, If you have a backup shell script, that copies files from local to remote server using rsync, you need the ability to rsync without having to enter the password.
To do that, setup ssh password less login as we explained earlier.

Example 5. Synchronize Files From Remote to Local

When you want to synchronize files from remote to local, specify remote path in source and local path in target as shown below.
$ rsync -avz thegeekstuff@192.168.200.10:/var/lib/rpm /root/temp
Password:
receiving file list ... done
rpm/
rpm/Basenames
.
sent 406 bytes  received 15810230 bytes  2432405.54 bytes/sec
total size is 45305958  speedup is 2.87

Example 6. Remote shell for Synchronization

rsync allows you to specify the remote shell which you want to use. You can use rsync ssh to enable the secured remote connection.
Use rsync -e ssh to specify which remote shell to use. In this case, rsync will use ssh.
$ rsync -avz -e ssh thegeekstuff@192.168.200.10:/var/lib/rpm /root/temp
Password:
receiving file list ... done
rpm/
rpm/Basenames

sent 406 bytes  received 15810230 bytes  2432405.54 bytes/sec
total size is 45305958  speedup is 2.87

Example 7. Do Not Overwrite the Modified Files at the Destination

In a typical sync situation, if a file is modified at the destination, we might not want to overwrite the file with the old file from the source.
Use rsync -u option to do exactly that. (i.e do not overwrite a file at the destination, if it is modified). In the following example, the file called Basenames is already modified at the destination. So, it will not be overwritten with rsync -u.
$ ls -l /root/temp/Basenames
total 39088
-rwxr-xr-x 1 root root        4096 Sep  2 11:35 Basenames

$ rsync -avzu thegeekstuff@192.168.200.10:/var/lib/rpm /root/temp
Password:
receiving file list ... done
rpm/

sent 122 bytes  received 505 bytes  114.00 bytes/sec
total size is 45305958  speedup is 72258.31

$ ls -lrt
total 39088
-rwxr-xr-x 1 root root        4096 Sep  2 11:35 Basenames

Example 8. Synchronize only the Directory Tree Structure (not the files)

Use rsync -d option to synchronize only directory tree from source to the destination. The below example, synchronize only directory tree in recursive manner, not the files in the directories.
$ rsync -v -d thegeekstuff@192.168.200.10:/var/lib/ .
Password:
receiving file list ... done
logrotate.status
CAM/
YaST2/
acpi/

sent 240 bytes  received 1830 bytes  318.46 bytes/sec
total size is 956  speedup is 0.46

Example 9. View the rsync Progress during Transfer

When you use rsync for backup, you might want to know the progress of the backup. i.e how many files are copies, at what rate it is copying the file, etc.
rsync –progress option displays detailed progress of rsync execution as shown below.
$ rsync -avz --progress thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ...
19 files to consider
./
Basenames
     5357568 100%   14.98MB/s    0:00:00 (xfer#1, to-check=17/19)
Conflictname
       12288 100%   35.09kB/s    0:00:00 (xfer#2, to-check=16/19)
.
.
.
sent 406 bytes  received 15810211 bytes  2108082.27 bytes/sec
total size is 45305958  speedup is 2.87
You can also use rsnapshot utility (that uses rsync) to backup local linux server, or backup remote linux server.

Example 10. Delete the Files Created at the Target

If a file is not present at the source, but present at the target, you might want to delete the file at the target during rsync.
In that case, use –delete option as shown below. rsync delete option deletes files that are not there in source directory.
# Source and target are in sync. Now creating new file at the target.
$ > new-file.txt

$ rsync -avz --delete thegeekstuff@192.168.200.10:/var/lib/rpm/ .
Password:
receiving file list ... done
deleting new-file.txt
./

sent 26 bytes  received 390 bytes  48.94 bytes/sec
total size is 45305958  speedup is 108908.55
Target has the new file called new-file.txt, when synchronize with the source with –delete option, it removed the file new-file.txt

Example 11. Do not Create New File at the Target

If you like, you can update (Sync) only the existing files at the target. In case source has new files, which is not there at the target, you can avoid creating these new files at the target. If you want this feature, use –existing option with rsync command.
First, add a new-file.txt at the source.
[/var/lib/rpm ]$ > new-file.txt
Next, execute the rsync from the target.
$ rsync -avz --existing root@192.168.1.2:/var/lib/rpm/ .
root@192.168.1.2's password:
receiving file list ... done
./

sent 26 bytes  received 419 bytes  46.84 bytes/sec
total size is 88551424  speedup is 198991.96
If you see the above output, it didn’t receive the new file new-file.txt

Example 12. View the Changes Between Source and Destination

This option is useful to view the difference in the files or directories between source and destination.
At the source:
$ ls -l /var/lib/rpm
-rw-r--r-- 1 root root  5357568 2010-06-24 08:57 Basenames
-rw-r--r-- 1 root root    12288 2008-05-28 22:03 Conflictname
-rw-r--r-- 1 root root  1179648 2010-06-24 08:57 Dirnames
At the destination:
$ ls -l /root/temp
-rw-r--r-- 1 root root    12288 May 28  2008 Conflictname
-rw-r--r-- 1 bin  bin   1179648 Jun 24 05:27 Dirnames
-rw-r--r-- 1 root root        0 Sep  3 06:39 Basenames
In the above example, between the source and destination, there are two differences. First, owner and group of the file Dirname differs. Next, size differs for the file Basenames.
Now let us see how rsync displays this difference. -i option displays the item changes.
$ rsync -avzi thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ... done
>f.st.... Basenames
.f....og. Dirnames

sent 48 bytes  received 2182544 bytes  291012.27 bytes/sec
total size is 45305958  speedup is 20.76
In the output it displays some 9 letters in front of the file name or directory name indicating the changes.
In our example, the letters in front of the Basenames (and Dirnames) says the following:
> specifies that a file is being transferred to the local host.
f represents that it is a file.
s represents size changes are there.
t represents timestamp changes are there.
o owner changed
g group changed.

Example 13. Include and Exclude Pattern during File Transfer

rsync allows you to give the pattern you want to include and exclude files or directories while doing synchronization.
$ rsync -avz --include 'P*' --exclude '*' thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ... done
./
Packages
Providename
Provideversion
Pubkeys

sent 129 bytes  received 10286798 bytes  2285983.78 bytes/sec
total size is 32768000  speedup is 3.19
In the above example, it includes only the files or directories starting with ‘P’ (using rsync include) and excludes all other files. (using rsync exclude ‘*’ )

Example 14. Do Not Transfer Large Files

You can tell rsync not to transfer files that are greater than a specific size using rsync –max-size option.
$ rsync -avz --max-size='100K' thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ... done
./
Conflictname
Group
Installtid
Name
Sha1header
Sigmd5
Triggername

sent 252 bytes  received 123081 bytes  18974.31 bytes/sec
total size is 45305958  speedup is 367.35
max-size=100K makes rsync to transfer only the files that are less than or equal to 100K. You can indicate M for megabytes and G for gigabytes.

Example 15. Transfer the Whole File

One of the main feature of rsync is that it transfers only the changed block to the destination, instead of sending the whole file.
If network bandwidth is not an issue for you (but CPU is), you can transfer the whole file, using rsync -W option. This will speed-up the rsync process, as it doesn’t have to perform the checksum at the source and destination.
#  rsync -avzW  thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp
Password:
receiving file list ... done
./
Basenames
Conflictname
Dirnames
Filemd5s
Group
Installtid
Name

sent 406 bytes  received 15810211 bytes  2874657.64 bytes/sec
total size is 45305958  speedup is 2.87

Steps to Setup User and Group Disk Quota on UNIX / Linux

On Linux, you can setup disk quota using one of the following methods:
  • File system base disk quota allocation
  • User or group based disk quota allocation
On the user or group based quota, following are three important factors to consider:
  • Hard limit – For example, if you specify 2GB as hard limit, user will not be able to create new files after 2GB
  • Soft limit – For example, if you specify 1GB as soft limit, user will get a warning message “disk quota exceeded”, once they reach 1GB limit. But, they’ll still be able to create new files until they reach the hard limit
  • Grace Period – For example, if you specify 10 days as a grace period, after user reach their hard limit, they would be allowed additional 10 days to create new files. In that time period, they should try to get back to the quota limit.

1. Enable quota check on filesystem

First, you should specify which filesystem are allowed for quota check.
Modify the /etc/fstab, and add the keyword usrquota and grpquota to the corresponding filesystem that you would like to monitor.
The following example indicates that both user and group quota check is enabled on /home filesystem
# cat /etc/fstab
LABEL=/home    /home   ext2   defaults,usrquota,grpquota  1 2
Reboot the server after the above change.

2. Initial quota check on Linux filesystem using quotacheck

Once you’ve enabled disk quota check on the filesystem, collect all quota information initially as shown below.
# quotacheck -avug
quotacheck: Scanning /dev/sda3 [/home] done
quotacheck: Checked 5182 directories and 31566 files
quotacheck: Old file not found.
quotacheck: Old file not found.
In the above command:
  • a: Check all quota-enabled filesystem
  • v: Verbose mode
  • u: Check for user disk quota
  • g: Check for group disk quota
The above command will create a aquota file for user and group under the filesystem directory as shown below.
# ls -l /home/

-rw-------    1 root     root        11264 Jun 21 14:49 aquota.user
-rw-------    1 root     root        11264 Jun 21 14:49 aquota.group

3. Assign disk quota to a user using edquota command

Use the edquota command as shown below, to edit the quota information for a specific user.
For example, to change the disk quota for user ‘ramesh’, use edquota command, which will open the soft, hard limit values in an editor as shown below.
# edquota ramesh

Disk quotas for user ramesh (uid 500):
  Filesystem           blocks       soft       hard     inodes     soft     hard
  /dev/sda3           1419352          0          0       1686        0        0
Once the edquota command opens the quota settings for the specific user in a editor, you can set the following limits:
  • soft and hard limit for disk quota size for the particular user.
  • soft and hard limit for the total number of inodes that are allowed for the particular user.

4. Report the disk quota usage for users and group using repquota

Use the repquota command as shown below to report the disk quota usage for the users and groups.
# repquota /home
*** Report for user quotas on device /dev/sda3
Block grace time: 7days; Inode grace time: 7days
                        Block limits                File limits
User            used    soft    hard  grace    used  soft  hard  grace
----------------------------------------------------------------------
root      --  566488       0       0           5401     0     0
nobody    --    1448       0       0             30     0     0
ramesh    -- 1419352       0       0           1686     0     0
john      --   26604       0       0            172     0     0

5. Add quotacheck to daily cron job

Add the quotacheck to the daily cron job. Create a quotacheck file as shown below under the /etc/cron.daily directory, that will run the quotacheck command everyday. This will send the output of the quotacheck command to root email address.
# cat /etc/cron.daily/quotacheck
quotacheck -avug

Troubleshooting Using dmesg Command in Unix and Linux

During system bootup process, kernel gets loaded into the memory and it controls the entire system.
When the system boots up, it prints number of messages on the screen that displays information about the hardware devices that the kernel detects during boot process.
These messages are available in kernel ring buffer and whenever the new message comes the old message gets overwritten. You could see all those messages after the system bootup using the dmesg command.

1. View the Boot Messages

By executing the dmesg command, you can view the hardwares that are detected during bootup process and it’s configuration details. There are lot of useful information displayed in dmesg. Just browse through them line by line and try to understand what it means. Once you have an idea of the kind of messages it displays, you might find it helpful for troubleshooting, when you encounter an issue.
# dmesg | more
Bluetooth: L2CAP ver 2.8
eth0: no IPv6 routers present
bnx2: eth0 NIC Copper Link is Down
usb 1-5.2: USB disconnect, address 5
bnx2: eth0 NIC Copper Link is Up, 100 Mbps full duplex
As we discussed earlier, you can also view hardware information using dmidecode.

2. View Available System Memory

You can also view the available memory from the dmesg messages as shown below.
# dmesg | grep Memory
Memory: 57703772k/60817408k available (2011k kernel code, 1004928k reserved, 915k data, 208k init)

3. View Ethernet Link Status (UP/DOWN)

In the example below, dmesg indicates that the eth0 link is in active state during the boot itself.
# dmesg  | grep eth
eth0: Broadcom NetXtreme II BCM5709 1000Base-T (C0) PCI Express found at mem 96000000, IRQ 169, node addr e4:1f:13:62:ff:58
eth1: Broadcom NetXtreme II BCM5709 1000Base-T (C0) PCI Express found at mem 98000000, IRQ 114, node addr e4:1f:13:62:ff:5a
eth0: Link up

4. Change the dmesg Buffer Size in /boot/config- file

Linux allows to you change the default size of the dmesg buffer. The CONFIG_LOG_BUF_SHIFT parameter in the /boot/config-2.6.18-194.el5 file (or similar file on your system) can be changed to modify the dmesg buffer.
The below value is in the power of 2. So, the buffer size in this example would be 262144 bytes. You can modify the buffer size based on your need (SUSE / REDHAT).
#  grep CONFIG_LOG_BUF_SHIFT  /boot/config-`uname -r`
CONFIG_LOG_BUF_SHIFT=18

5. Clear Messages in dmesg Buffer

Sometimes you might want to clear the dmesg messages before your next reboot. You can clear the dmesg buffer as shown below.
# dmesg -c

# dmesg

6. dmesg timestamp: Date and Time of Each Boot Message in dmesg

By default the dmesg don’t have the timestamp associated with them. However Linux provides a way to see the date and time for each boot messages in dmesg in the /var/log/kern.log file as shown below.
klogd service should be enabled and configured properly to log the messages in /var/log/kern.log file.
# dmesg | grep "L2 cache"
[    0.014681] CPU: L2 cache: 2048K

# grep "L2 cache" kern.log.1
Oct 18 23:55:40 ubuntu kernel: [    0.014681] CPU: L2 cache: 2048K

RPM Command: 15 Examples to Install, Uninstall, Upgrade, Query RPM Packages

RPM command is used for installing, uninstalling, upgrading, querying, listing, and checking RPM packages on your Linux system.
RPM stands for Red Hat Package Manager.
With root privilege, you can use the rpm command with appropriate options to manage the RPM software packages.
In this article, let us review 15 practical examples of rpm command.
Let us take an rpm of Mysql Client and run through all our examples.

1. Installing a RPM package Using rpm -ivh

RPM filename has packagename, version, release and architecture name.
For example, In the MySQL-client-3.23.57-1.i386.rpm file:
  • MySQL-client – Package Name
  • 3.23.57 – Version
  • 1 – Release
  • i386 – Architecture
When you install a RPM, it checks whether your system is suitable for the software the RPM package contains, figures out where to install the files located inside the rpm package, installs them on your system, and adds that piece of software into its database of installed RPM packages.
The following rpm command installs Mysql client package.
# rpm -ivh  MySQL-client-3.23.57-1.i386.rpm
Preparing...                ########################################### [100%]
   1:MySQL-client           ########################################### [100%]
rpm command and options
  • -i : install a package
  • -v : verbose
  • -h : print hash marks as the package archive is unpacked.
You can also use dpkg on Debian, pkgadd on Solaris, depot on HP-UX to install packages.

2. Query all the RPM Packages using rpm -qa

You can use rpm command to query all the packages installed in your system.
# rpm -qa
cdrecord-2.01-10.7.el5
bluez-libs-3.7-1.1
setarch-2.0-1.1
.
.
  • -q query operation
  • -a queries all installed packages
To identify whether a particular rpm package is installed on your system, combine rpm and grep command as shown below. Following command checks whether cdrecord package is installed on your system.
# rpm -qa | grep 'cdrecord'

3. Query a Particular RPM Package using rpm -q

The above example lists all currently installed package. After installation of a package to check the installation, you can query a particular package and verify as shown below.
# rpm -q MySQL-client
MySQL-client-3.23.57-1

# rpm -q MySQL
package MySQL is not installed
Note: To query a package, you should specify the exact package name. If the package name is incorrect, then rpm command will report that the package is not installed.

4. Query RPM Packages in a various format using rpm –queryformat

Rpm command provides an option –queryformat, which allows you to give the header tag names, to list the packages. Enclose the header tag with in {}.
# rpm -qa --queryformat '%{name-%{version}-%{release} %{size}\n'
cdrecord-2.01-10.7 12324
bluez-libs-3.7-1.1 5634
setarch-2.0-1.1 235563
.
.

#

5. Which RPM package does a file belong to? – Use rpm -qf

Let us say, you have list of files and you would want to know which package owns all these files. rpm command has options to achieve this.
The following example shows that /usr/bin/mysqlaccess file is part of the MySQL-client-3.23.57-1 rpm.
# rpm -qf /usr/bin/mysqlaccess
MySQL-client-3.23.57-1
  • -f : file name

6. Locate documentation of a package that owns file using rpm -qdf

Use the following to know the list of documentations, for a package that owns a file. The following command, gives the location of all the manual pages related to mysql package.
# rpm -qdf /usr/bin/mysqlaccess
/usr/share/man/man1/mysql.1.gz
/usr/share/man/man1/mysqlaccess.1.gz
/usr/share/man/man1/mysqladmin.1.gz
/usr/share/man/man1/mysqldump.1.gz
/usr/share/man/man1/mysqlshow.1.gz
  • -d : refers documentation.

7. Information about Installed RPM Package using rpm -qi

rpm command provides a lot of information about an installed pacakge using rpm -qi as shown below:
# rpm -qi MySQL-client
Name        : MySQL-client                 Relocations: (not relocatable)
Version     : 3.23.57                           Vendor: MySQL AB
Release     : 1                             Build Date: Mon 09 Jun 2003 11:08:28 PM CEST
Install Date: Mon 06 Feb 2010 03:19:16 AM PST               Build Host: build.mysql.com
Group       : Applications/Databases        Source RPM: MySQL-3.23.57-1.src.rpm
Size        : 5305109                          License: GPL / LGPL
Signature   : (none)
Packager    : Lenz Grimmer
URL         : http://www.mysql.com/
Summary     : MySQL - Client
Description : This package contains the standard MySQL clients.
If you have an RPM file that you would like to install, but want to know more information about it before installing, you can do the following:
# rpm -qip MySQL-client-3.23.57-1.i386.rpm
Name        : MySQL-client                 Relocations: (not relocatable)
Version     : 3.23.57                           Vendor: MySQL AB
Release     : 1                             Build Date: Mon 09 Jun 2003 11:08:28 PM CEST
Install Date: (not installed)               Build Host: build.mysql.com
Group       : Applications/Databases        Source RPM: MySQL-3.23.57-1.src.rpm
Size        : 5305109                          License: GPL / LGPL
Signature   : (none)
Packager    : Lenz Grimmer
URL         : http://www.mysql.com/
Summary     : MySQL - Client
Description : This package contains the standard MySQL clients.
  • -i : view information about an rpm
  • -p : specify a package name

8. List all the Files in a Package using rpm -qlp

To list the content of a RPM package, use the following command, which will list out the files without extracting into the local directory folder.
$ rpm -qlp ovpc-2.1.10.rpm
/usr/bin/mysqlaccess
/usr/bin/mysqldata
/usr/bin/mysqlperm
.
.
/usr/bin/mysqladmin
  • q : query the rpm file
  • l : list the files in the package
  • p : specify the package name
You can also extract files from RPM package using rpm2cpio as we discussed earlier.

9. List the Dependency Packages using rpm -qRP

To view the list of packages on which this package depends,
# rpm -qRp MySQL-client-3.23.57-1.i386.rpm
/bin/sh
/usr/bin/perl

10. Find out the state of files in a package using rpm -qsp

The following command is to find state (installed, replaced or normal) for all the files in a RPM package.
# rpm -qsp MySQL-client-3.23.57-1.i386.rpm
normal        /usr/bin/msql2mysql
normal        /usr/bin/mysql
normal        /usr/bin/mysql_find_rows
normal        /usr/bin/mysqlaccess
normal        /usr/bin/mysqladmin
normal        /usr/bin/mysqlbinlog
normal        /usr/bin/mysqlcheck
normal        /usr/bin/mysqldump
normal        /usr/bin/mysqlimport
normal        /usr/bin/mysqlshow
normal        /usr/share/man/man1/mysql.1.gz
normal        /usr/share/man/man1/mysqlaccess.1.gz
normal        /usr/share/man/man1/mysqladmin.1.gz
normal        /usr/share/man/man1/mysqldump.1.gz
normal        /usr/share/man/man1/mysqlshow.1.gz

11. Verify a Particular RPM Package using rpm -Vp

Verifying a package compares information about the installed files in the package with information about the files taken from the package metadata stored in the rpm database. In the following command, -V is for verification and -p option is used to specify a package name to verify.
# rpm -Vp MySQL-client-3.23.57-1.i386.rpm
S.5....T c        /usr/bin/msql2mysql
S.5....T c        /usr/bin/mysql
S.5....T c        /usr/bin/mysql_find_rows
S.5....T c        /usr/bin/mysqlaccess
The character in the above output denotes the following:
  • S file Size differs
  • M Mode differs (includes permissions and file type)
  • 5 MD5 sum differs
  • D Device major/minor number mismatch
  • L readlink(2) path mismatch
  • U User ownership differs
  • G Group ownership differs
  • T mTime differs

12. Verify a Package Owning file using rpm -Vf

The following command verify the package which owns the given filename.
# rpm -Vf /usr/bin/mysqlaccess
S.5....T c /usr/bin/mysql
#

13. Upgrading a RPM Package using rpm -Uvh

Upgrading a package is similar to installing one, but RPM automatically un-installs existing versions of the package before installing the new one. If an old version of the package is not found, the upgrade option will still install it.
# rpm -Uvh MySQL-client-3.23.57-1.i386.rpm
Preparing...    ########################################### [100%]
1:MySQL-client          ###########################################

14. Uninstalling a RPM Package using rpm -e

To remove an installed rpm package using -e as shown below. After uninstallation, you can query using rpm -qa and verify the uninstallation.
# rpm -ev MySQL-client

15. Verifying all the RPM Packages using rpm -Va

The following command verifies all the installed packages.
# rpm -Va
S.5....T c /etc/issue
S.5....T c /etc/issue.net
S.5....T c /var/service/imap/ssl/seed
S.5....T c /home/httpd/html/horde/ingo/config/backends.php
.
.
S.5....T c /home/httpd/html/horde/ingo/config/prefs.php
S.5....T c /etc/printcap

UNIX / Linux: 10 Netstat Command Examples

Netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc.,
In this article, let us review 10 practical unix netstat command examples.

1. List All Ports (both listening and non listening ports)

List all ports using netstat -a

# netstat -a | more
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:30037         *:*                     LISTEN
udp        0      0 *:bootpc                *:*                                

Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     6135     /tmp/.X11-unix/X0
unix  2      [ ACC ]     STREAM     LISTENING     5140     /var/run/acpid.socket

List all tcp ports using netstat -at

# netstat -at
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:30037         *:*                     LISTEN
tcp        0      0 localhost:ipp           *:*                     LISTEN
tcp        0      0 *:smtp                  *:*                     LISTEN
tcp6       0      0 localhost:ipp           [::]:*                  LISTEN

List all udp ports using netstat -au

# netstat -au
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
udp        0      0 *:bootpc                *:*
udp        0      0 *:49119                 *:*
udp        0      0 *:mdns                  *:*

2. List Sockets which are in Listening State

List only listening ports using netstat -l

# netstat -l
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:ipp           *:*                     LISTEN
tcp6       0      0 localhost:ipp           [::]:*                  LISTEN
udp        0      0 *:49119                 *:*

List only listening TCP Ports using netstat -lt

# netstat -lt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:30037         *:*                     LISTEN
tcp        0      0 *:smtp                  *:*                     LISTEN
tcp6       0      0 localhost:ipp           [::]:*                  LISTEN

List only listening UDP Ports using netstat -lu

# netstat -lu
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
udp        0      0 *:49119                 *:*
udp        0      0 *:mdns                  *:*

List only the listening UNIX Ports using netstat -lx

# netstat -lx
Active UNIX domain sockets (only servers)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     6294     private/maildrop
unix  2      [ ACC ]     STREAM     LISTENING     6203     public/cleanup
unix  2      [ ACC ]     STREAM     LISTENING     6302     private/ifmail
unix  2      [ ACC ]     STREAM     LISTENING     6306     private/bsmtp

3. Show the statistics for each protocol

Show statistics for all ports using netstat -s

# netstat -s
Ip:
    11150 total packets received
    1 with invalid addresses
    0 forwarded
    0 incoming packets discarded
    11149 incoming packets delivered
    11635 requests sent out
Icmp:
    0 ICMP messages received
    0 input ICMP message failed.
Tcp:
    582 active connections openings
    2 failed connection attempts
    25 connection resets received
Udp:
    1183 packets received
    4 packets to unknown port received.
.....

Show statistics for TCP (or) UDP ports using netstat -st (or) -su

# netstat -st

# netstat -su

4. Display PID and program names in netstat output using netstat -p

netstat -p option can be combined with any other netstat option. This will add the “PID/Program Name” to the netstat output. This is very useful while debugging to identify which program is running on a particular port.
# netstat -pt
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        1      0 ramesh-laptop.loc:47212 192.168.185.75:www        CLOSE_WAIT  2109/firefox
tcp        0      0 ramesh-laptop.loc:52750 lax:www ESTABLISHED 2109/firefox

5. Don’t resolve host, port and user name in netstat output

When you don’t want the name of the host, port or user to be displayed, use netstat -n option. This will display in numbers, instead of resolving the host name, port name, user name.
This also speeds up the output, as netstat is not performing any look-up.
# netstat -an
If you don’t want only any one of those three items ( ports, or hosts, or users ) to be resolved, use following commands.
# netsat -a --numeric-ports

# netsat -a --numeric-hosts

# netsat -a --numeric-users

6. Print netstat information continuously

netstat will print information continuously every few seconds.
# netstat -c
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 ramesh-laptop.loc:36130 101-101-181-225.ama:www ESTABLISHED
tcp        1      1 ramesh-laptop.loc:52564 101.11.169.230:www      CLOSING
tcp        0      0 ramesh-laptop.loc:43758 server-101-101-43-2:www ESTABLISHED
tcp        1      1 ramesh-laptop.loc:42367 101.101.34.101:www      CLOSING
^C

7. Find the non supportive Address families in your system

netstat --verbose
At the end, you will have something like this.
 netstat: no support for `AF IPX' on this system.
 netstat: no support for `AF AX25' on this system.
 netstat: no support for `AF X25' on this system.
 netstat: no support for `AF NETROM' on this system.

8. Display the kernel routing information using netstat -r

# netstat -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.1.0     *               255.255.255.0   U         0 0          0 eth2
link-local      *               255.255.0.0     U         0 0          0 eth2
default         192.168.1.1     0.0.0.0         UG        0 0          0 eth2
Note: Use netstat -rn to display routes in numeric format without resolving for host-names.

9. Find out on which port a program is running

# netstat -ap | grep ssh
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
tcp        1      0 dev-db:ssh           101.174.100.22:39213        CLOSE_WAIT  -
tcp        1      0 dev-db:ssh           101.174.100.22:57643        CLOSE_WAIT  -
Find out which process is using a particular port:
# netstat -an | grep ':80'

10. Show the list of network interfaces

# netstat -i
Kernel Interface table
Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0       1500 0         0      0      0 0             0      0      0      0 BMU
eth2       1500 0     26196      0      0 0         26883      6      0      0 BMRU
lo        16436 0         4      0      0 0             4      0      0      0 LRU
Display extended information on the interfaces (similar to ifconfig) using netstat -ie:
# netstat -ie
Kernel Interface table
eth0      Link encap:Ethernet  HWaddr 00:10:40:11:11:11
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Memory:f6ae0000-f6b00000

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


Debian 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.

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

Linux ethtool Examples to Manipulate Ethernet Card (NIC Card)

Ethtool 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 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

6 Common Errors in Setting Java Heap Size


Two JVM options are often used to tune JVM heap size: -Xmx for maximum heap size, and -Xms for initial heap size. Here are some common mistakes I have seen when using them:

* Missing m, M, g or G at the end (they are case insensitive). For example,


java -Xmx128 BigApp
java.lang.OutOfMemoryError: Java heap space


The correct command should be: java -Xmx128m BigApp. To be precise, -Xmx128 is a valid setting for very small apps, like HelloWorld. But in real life, I guess you really mean

-Xmx128m

* Extra space in JVM options, or incorrectly use =. For example,


java -Xmx 128m BigApp

Invalid maximum heap size: -Xmx

Could not create the Java virtual machine.

java -Xmx=512m HelloWorld

Invalid maximum heap size: -Xmx=512m


Could not create the Java virtual machine.

The correct command should be java -Xmx128m BigApp, with no whitespace nor =. -X options are different than -Dkey=value system properties, where = is used.

* Only setting -Xms JVM option and its value is greater than the default maximum heap size, which is 64m. The default minimum heap size seems to be 0. For example,

java -Xms128m BigApp

Error occurred during initialization of VM

Incompatible initial and maximum heap sizes specified

The correct command should be java -Xms128m -Xmx128m BigApp. It’s a good idea to set the minimum and maximum heap size to the same value. In any case, don’t let the minimum heap size exceed the maximum heap size.

* Heap size is larger than your computer’s physical memory. For example,

java -Xmx2g BigApp

Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.
The fix is to make it lower than the physical memory: java -Xmx1g BigApp

* Incorrectly use mb as the unit, where m or M should be used instead.


java -Xms256mb -Xmx256mb BigApp

Invalid initial heap size: -Xms256mb

Could not create the Java virtual machine.

* The heap size is larger than JVM thinks you would ever need. For example,

java -Xmx256g BigApp

Invalid maximum heap size: -Xmx256g

The specified size exceeds the maximum representable size.
Could not create the Java virtual machine.
The fix is to lower it to a reasonable value: java -Xmx256m BigApp

* The value is not expressed in whole number. For example,

java -Xmx0.9g BigApp

Invalid maximum heap size: -Xmx0.9g

Could not create the Java virtual machine.

The correct command should be java -Xmx928m BigApp

NOTE:

How to set java heap size in Tomcat?


Stop Tomcat server, set environment variable CATALINA_OPTS, and then restart Tomcat. Look at the file tomcat-install/bin/catalina.sh or catalina.bat for how this variable is used. For example,

set CATALINA_OPTS=”-Xms512m -Xmx512m”  (Windows)
export CATALINA_OPTS=”-Xms512m -Xmx512m”  (ksh/bash)
setenv CATALINA_OPTS “-Xms512m -Xmx512m”  (tcsh/csh)


In catalina.bat or catallina.sh, you may have noticed CATALINA_OPTS, JAVA_OPTS, or both can be used to specify Tomcat JVM options. What is the difference between CATALINA_OPTS and JAVA_OPTS? The name CATALINA_OPTS is specific for Tomcat servlet container, whereas JAVA_OPTS may be used by other java applications (e.g., JBoss). Since environment variables are shared by all applications, we don’t want Tomcat to inadvertently pick up the JVM options intended for other apps. I prefer to use CATALINA_OPTS.

How to set java heap size in JBoss?

Stop JBoss server, edit $JBOSS_HOME/bin/run.conf, and then restart JBoss server. You can change the line with JAVA_OPTS to something like:

JAVA_OPTS=”-server -Xms128m -Xmx128m”

How to set java heap size in Eclipse?

You have 2 options:
  1. Edit eclipse-home/eclipse.ini to be something like the following and restart Eclipse.

    -vmargs
    -Xms64m
    -Xmx256m
  2. Or, you can just run eclipse command with additional options at the very end. Anything after -vmargs will be treated as JVM options and passed directly to the JVM. JVM options specified in the command line this way will always override those in eclipse.ini. For example,

    eclipse -vmargs -Xms64m -Xmx256m

How to set java heap size in NetBeans?

Exit NetBeans, edit the file netbeans-install/etc/netbeans.conf. For example,

netbeans_default_options=”-J-Xms512m -J-Xmx512m -J-XX:PermSize=32m -J-XX:MaxPermSize=128m -J-Xverify:none

How to set java heap size in Apache Ant?

Set environment variable ANT_OPTS. Look at the file $ANT_HOME/bin/ant or %ANT_HOME%\bin\ant.bat, for how this variable is used by Ant runtime.

set ANT_OPTS=”-Xms512m -Xmx512m”  (Windows)
export ANT_OPTS=”-Xms512m -Xmx512m”  (ksh/bash)
setenv ANT_OPTS “-Xms512m -Xmx512m”  (tcsh/csh)

How to set java heap size in jEdit?

jEdit is a java application, and basically you need to set minimum/maximum heap size JVM options when you run java command. jEdit by default runs with a default maximum heap size 64m. When you work on large files, you are likely to get these errors:

java.lang.OutOfMemoryError: Java heap space
at java.lang.String.concat(String.java:2001)
at org.gjt.sp.jedit.buffer.UndoManager.contentInserted(UndoManager.java:160)
at org.gjt.sp.jedit.Buffer.insert(Buffer.java:1139)
at org.gjt.sp.jedit.textarea.JEditTextArea.setSelectedText(JEditTextArea.java:2052)
at org.gjt.sp.jedit.textarea.JEditTextArea.setSelectedText(JEditTextArea.java:2028)
at org.gjt.sp.jedit.Registers.paste(Registers.java:263)


How to fix it? If you click a desktop icon, or Start menu item to start jEdit: right-click the icon or menu item, view its property, and you can see its target is something like:

C:\jdk6\bin\javaw.exe -jar “C:\jedit\jedit.jar”

You can change that line to:

C:\jdk6\bin\javaw.exe -Xmx128m -Xms128m -jar “C:\jedit\jedit.jar”

If you run a script to start jEdit: just add these JVM options to the java line inside the script file:

java -Xmx128m -Xms128m -jar jedit.jar

If you start jEdit by running java command: just add these JVM options to your java command:

java -Xmx128m -Xms128m -jar jedit.jar

Note that when you run java with -jar option, anything after -jar jar-file will be treated as application arguments. So you should always put JVM options before -jar. Otherwise, you will get error:

C:\jedit>java -jar jedit.jar -Xmx128m

Unknown option: -Xmx128m

Usage: jedit [] []