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remote server

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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How To Reuse SSH Connection To Speed Up Remote Login Process

Q. How do I reuse same ssh connection to speed up remote login procedure with OpenSSH client?
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Reboot Linux System Command

How do I reboot my Linux based system? How do I reboot a remote Linux system or server using command line?
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Debian Linux Stop Iptables Firewall

H do I stop Iptables firewall under Debian Linux server system?
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I'd like to configure my Debian box to backup two remote servers using rsnapshot software. It should make incremental snapshots of local and remote filesystems for any number of machines on 2nd hard disk located at /disk1 ( /dev/sdb2).
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Fingerprint / Identify Remote Web Server

Q. How do I fingerprint or identify remove web server a from UNIX / Linux shell prompt?
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Mac OS X Remove SSH Known Host

I've reinstalled Linux on remote server and now trying to connect it over ssh using Mac OS X:
ssh user@server1.example.com

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

Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
Please contact your system administrator.
Add correct host key in /Users/user/.ssh/known_hosts to get rid of this message.
Offending key in /Users/user/.ssh/known_hosts:1
RSA host key for server1.example.com has changed and you have requested strict checking.
Host key verification failed.

How do I fix this problem under Mac OX X?
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Turn on telnet server on Debian Linux

Q. How do I install and turn on telnet server on Debian Linux VPS Server?

A. I don't recommend using telnet at all on VPS or any other Linux / UNIX server. Telnet transfers all data including passwords in clear text format. It is recommended that you use ssh which is installed by default.

Use ssh and connect to remote server called boo.myvps.com, enter:
ssh user@boo.myvps.com
ssh root@boo.myvps.com
ssh root@server-ip-address

In case you still need telnet, type the following two commands (not recommended
# apt-get install telnetd
# /etc/init.d/inetd restart
$ telnet server-ip-address

How to backup the remote files in Linux / UNIX

Q. How do I make remote backups under Linux? I’ve CentOS 5 Linux server located in remote data center and I’d like to backup it to local or another server?

A. Both Linux / UNIX come with handy tools to make secure remote backups. You can use tool called rsync for automating remote backups of your Linux, UNIX, Windows server, Mac OS X and BSD systems. rsync is a program with many more options and uses the rsync remote-update protocol to greatly speed up file transfers when the destination file is being updated.

Task: Copy files / backup files from remote Linux server

Let us say you would like to backup files from remote server called server.nixcraft.in and directory called /home/vivek to local directory called /backup, type the command as follows on local system:
$ rsync -avz -e ssh vivek@server.nixcraft.in:/home/vivek/ /backup
You need to supply password for vivek user.

Task: Exclude files from backup

You can also skip few files from backup. Let us say you don't want to backup all C source code file, enter:
$ rsync --exclude '*.cpp' -avz -e ssh vivek@server.nixcraft.in:/home/vivek/ /backup

Task: Automatic backup using a shell script

SSH always prompts for a password. To automate process via a shell script you need to remove password using SSH key i.e. generate passphraseless keys, enter (type at local system):
$ ssh-keygen -t dsa
When asked for to enter passphrase, just press [ENTER] key twice. Now copy public key to remote server:
$ scp ~/.ssh/id_dsa.pub vivek@server.nixcraft.in:.ssh/authorized_keys
Now you can login without a password. For more information see - howto setup SSH with DSA public key authentication and RSA key authentication for password less login.

Now create a simple shell script as follows:
$ vi backup.sh
Append code:
rsync --exclude '*.cpp' --exclude '*.log' -avz -e ssh vivek@server.nixcraft.in:/home/vivek/ /backup

Setup executable permission using chmod command:
$ chmod +x backup.sh
Use cron to command to backup remote server:
$ crontab -e
Make a backup everyday:
@daily /path/to/backup.sh
Save and close the file.

Howto install duplicity rpm under RedHat / CentOS / Fedora Core Linux

Q. I would like to use duplicity package to automatically encrypting and storing remote backups in a bandwidth efficient manner in our backup server. The server is already configured and I’d like to install the same under RedHat Enterprise Linux. How do I install duplicity w/o compiling from source code?

A. Duplicity is a piece of software which provides easy encrypted versioned remote backup of files requiring little of the remote server. It does this using GnuPG, tar, and rdiff. To transmit data it can use ssh/scp, local file access, rsync, ftp, and Amazon S3.

The best way to install it to use rpm files from DAG's repo. For example RHEL 4 64 bit version can be installed using RPM command:
# wget http://dag.wieers.com/rpm/packages/duplicity/duplicity-0.4.2-1.el4.rf.x86_64.rpm
# rpm -ivh duplicity-0.4.2-1.el4.rf.x86_64.rpm

In order to use duplicity you need to create a GPG key:
# gpg --gen-key
Next run duplicity as follows to make backups:
# duplicity --encrypt-key="YOUR-KEY" /home scp://user@backup.server.com/directory
You can verify backups with --verify option:
# duplicity --encrypt-key="YOUR-KEY" --verify scp://user@backup.server.com/directory /home

Finally, if you need to restore file use command as follows:
# mkdir -p /disk3/resored.file
# duplicity --encrypt-key="YOUR-KEY" scp://user@backup.server.com/directory /disk3/resored.file

Read the man page of duplicity and gpg for more information and command options.