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Linux X11 Connection Rejected Because of Wrong Authentication Error and Solution

Q. I'm trying to login to my remote Ubuntu Linux server from Mac OS X desktop using following command:
ssh -X user@vpn.officeserver.example.com xeyes

But I'm getting an error that read as follows:

X11 connection rejected because of wrong authentication.

How do I fix this error?
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Linux / UNIX: Create Large 1GB Binary Image File With dd Command

How do I create 1 GB or 10 GB image file instantly with dd command under UNIX / Linux / BSD operating systems using a shell prompt?
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nslookup / host Dns Client Testing Command Not Found on Debian / Ubuntu Linux

Q. I'm not able to run nslookup or host command under Debian or Ubuntu Linux. In fact, these commands are missing from my installation. How do I install nslookup and related dns client commands?
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Debian / Ubuntu Linux: List All Packages Which Could be Updated and Applied to System

Q. How do I know what packages are available to be updated on my Debian / Ubuntu Linux system?

A. You can use standard command line utility called apt-get or GUI tool called Synaptic Update-Manager.

List all packages which could be updated

To list outdated package use apt-get command has following two options:
=> -u : Show upgraded packages; Print out a list of all packages that are to be upgraded.
=> upgrade : It is used to install the newest versions of all packages currently installed on the system

Type the following command at shell prompt:
$ sudo apt-get upgrade
$ sudo apt-get -i upgrade


Reading package lists... Done
Building dependency tree... Done
The following packages will be upgraded:
  debconf debconf-i18n e2fslibs e2fsprogs file findutils klibc-utils libblkid1 libc6 libc6-i686 libcomerr2 libklibc libkrb53 libmagic1
  libpam-modules libpam-runtime libpam0g libss2 libssl0.9.8 libuuid1 linux-image-2.6-686 linux-image-2.6.18-5-686 locales perl perl-base
  perl-modules tar tzdata
28 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 39.6MB of archives.
After unpacking 148kB of additional disk space will be used.
Do you want to continue [Y/n]?

To updated just say yes to prompt - "Do you want to continue". Alternatively, you can type the following command:
$ sudo apt-get update
$ sudo apt-get upgrade

Synaptic GUI Package Update Notifier

Synaptic works hand-in-hand with Update-Manager to inform you about updates to the software installed on your system. If software or security updates are available, Update-Manager will display a pop-up message and an icon in the notification area on your GNOME desktop. To update your system, click on the notification icon, enter your password and click OK.
How to keep your Ubuntu / Debian system up-to-date
(Fig. 01: Synaptic GUI Package Update Notifier [ Image credit Ubuntu Project] )

Howto Find Out or Learn Harddisk Size in Linux or UNIX

How do I find out my installed hard disk size in Linux or UNIX like operating systems?
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How do I rotate log files?

Q. How do I rotate log files under Linux operating system?

A. You need use tool called logrotate, which is designed to ease administration of systems that generate large numbers of log files. It allows automatic rotation, compression, removal, and mailing of log files.

Each log file may be handled daily, weekly, monthly, or when it grows too large. With this tool you keep logs longer with less disk space.

Default configuration file

The default configuration file is /etc/logrotate.conf:
# see "man logrotate" for details
# rotate log files weekly
# keep 4 weeks worth of backlogs
rotate 4
# create new (empty) log files after rotating old ones
# uncomment this if you want your log files compressed
# RPM packages drop log rotation information into this directory
include /etc/logrotate.d
# no packages own wtmp -- we'll rotate them here
/var/log/wtmp {
create 0664 root utmp
rotate 1
Service or server specific configurations stored in /etc/logrotate.d directory, for example here is sample apache logrotate configuration file:# cat /etc/logrotate.d/httpdOutput:

/var/log/httpd/*.log {
 rotate 52
      /bin/kill -HUP `cat /var/run/httpd.pid 2>/dev/null` 2> /dev/null || true    endscript


  • weekly : Log files are rotated if the current weekday is less then the weekday of the last rotation or if more then a week has passed since the last rotation.
  • rotate 52 : Log files are rotated 52 times before being removed or mailed to the address specified in a mail directive. If count is 0, old versions are removed rather then rotated.
  • compress : Old versions of log files are compressed with gzip to save disk space.
  • missingok : If the log file is missing, go on to the next one without issuing an error message.
  • notifempty : Do not rotate the log if it is empty
  • sharedscripts : Normally, prerotate and postrotate scripts are run for each log which is rotated, meaning that a single script may be run multiple times for log file entries which match multiple files. If sharedscript is specified, the scripts are only run once, no matter how many logs match the wildcarded pattern. However, if none of the logs in the pattern require rotating, the scripts will not be run at all.
  • postrotate
    /bin/kill -HUP `cat /var/run/httpd.pid 2>/dev/null` 2> /dev/null || true
    endscript : The lines between postrotate and endscript (both of which must appear on lines by themselves) are executed after the log file is rotated. These directives may only appear inside a log file definition.

See complete working example: How to rotating logs with logrotate for Lighttpd web server.

How Do I Find The Largest Top 10 Files and Directories On a Linux / UNIX / BSD?

How do I find the largest top files and directories on a Linux or Unix like operating systems?
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