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ssh key oluşturma ve izin verme

How To Set Up SSH Keys

About SSH Keys

SSH keys provide a more secure way of logging into a virtual private server with SSH than using a password alone. While a password can eventually be cracked with a brute force attack, SSH keys are nearly impossible to decipher by brute force alone. Generating a key pair provides you with two long string of characters: a public and a private key. You can place the public key on any server, and then unlock it by connecting to it with a client that already has the private key. When the two match up, the system unlocks without the need for a password. You can increase security even more by protecting the private key with a passphrase.

Step One—Create the RSA Key Pair

The first step is to create the key pair on the client machine (there is a good chance that this will just be your computer):

ssh-keygen -t rsa

Step Two—Store the Keys and Passphrase

Once you have entered the Gen Key command, you will get a few more questions:

Enter file in which to save the key (/home/demo/.ssh/id_rsa):

You can press enter here, saving the file to the user home (in this case, my example user is called demo).

Enter passphrase (empty for no passphrase):

It’s up to you whether you want to use a passphrase. Entering a passphrase does have its benefits: the security of a key, no matter how encrypted, still depends on the fact that it is not visible to anyone else. Should a passphrase-protected private key fall into an unauthorized users possession, they will be unable to log in to its associated accounts until they figure out the passphrase, buying the hacked user some extra time. The only downside, of course, to having a passphrase, is then having to type it in each time you use the Key Pair.

The entire key generation process looks like this:

ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/demo/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/demo/.ssh/id_rsa.
Your public key has been saved in /home/demo/.ssh/id_rsa.pub.
The key fingerprint is:
4a:dd:0a:c6:35:4e:3f:ed:27:38:8c:74:44:4d:93:67 demo@a
The key's randomart image is:
+--[ RSA 2048]----+
|          .oo.   |
|         .  o.E  |
|        + .  o   |
|     . = = .     |
|      = S = .    |
|     o + = +     |
|      . o + o .  |
|           . o   |
|                 |
+-----------------+

The public key is now located in /home/demo/.ssh/id_rsa.pub
The private key (identification) is now located in /home/demo/.ssh/id_rsa

Step Three—Copy the Public Key

Once the key pair is generated, it’s time to place the public key on the virtual server that we want to use.

You can copy the public key into the new machine’s authorized_keys file with the ssh-copy-id command. Make sure to replace the example username and IP address below.

ssh-copy-id user@123.45.56.78

Alternatively, you can paste in the keys using SSH:

cat ~/.ssh/id_rsa.pub | ssh user@123.45.56.78 "mkdir -p ~/.ssh && cat >>  ~/.ssh/authorized_keys"

No matter which command you chose, you should see something like:

The authenticity of host '12.34.56.78 (12.34.56.78)' can't be established.
RSA key fingerprint is b1:2d:33:67:ce:35:4d:5f:f3:a8:cd:c0:c4:48:86:12.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '12.34.56.78' (RSA) to the list of known hosts.
user@12.34.56.78's password: 
Now try logging into the machine, with "ssh 'user@12.34.56.78'", and check in:

  ~/.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

Now you can go ahead and log into user@12.34.56.78 and you will not be prompted for a password. However, if you set a passphrase, you will be asked to enter the passphrase at that time (and whenever else you log in in the future).

Optional Step Four—Disable the Password for Root Login

Once you have copied your SSH keys unto your server and ensured that you can log in with the SSH keys alone, you can go ahead and restrict the root login to only be permitted via SSH keys.

In order to do this, open up the SSH config file:

sudo nano /etc/ssh/sshd_config

Within that file, find the line that includes PermitRootLogin and modify it to ensure that users can only connect with their SSH key:

PermitRootLogin without-password

Put the changes into effect:

reload ssh

Digital Ocean Addendum

The Digital Ocean control allows you to add public keys to your new droplets when they’re created. You can generate the SSH Key in a convenient location, such as the computer, and then upload the public key to the SSH key section.

Then, when you create a new VPS, you can choose to include that public key on the server. No root password will be emailed to you and you can log in to your new virtual private server from your chosen client. If you created a passphrase, you will be prompted to enter that upon login.

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Posted by on 30 Mayıs 2015 in Linux

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Linux’ta Dosyaları büyüklüğe göre sıralamak

Bulunduğunuz dizindeki dosyaları ve klasörleri(alt klasörler dahil) büyüklüğüne göre sıralamak için aşagıkaki komutu kullanabilirsiniz.

du -s * | sort -nr | cut -f2- | xargs du -hs

 

Posted by on 24 Ağustos 2014 in Bilgisayar, Linux

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DBERROR db4: /var/lib/imap/deliver.db: unexpected file type or format

Problem:

Aug 23 17:37:50 localhost master[16716]: about to exec /usr/lib/cyrus-imapd/lmtpd
Aug 23 17:37:50 localhost lmtpunix[16716]: executed
Aug 23 17:37:50 localhost lmtpunix[16716]: DBERROR db4: /var/lib/imap/deliver.db: unexpected file type or format
Aug 23 17:37:50 localhost lmtpunix[16716]: DBERROR: opening /var/lib/imap/deliver.db: Invalid argument
Aug 23 17:37:50 localhost lmtpunix[16716]: DBERROR: opening /var/lib/imap/deliver.db: cyrusdb error
Aug 23 17:37:50 localhost lmtpunix[16716]: FATAL: lmtpd: unable to init duplicate delivery database
Aug 23 17:37:50 localhost master[3545]: process 16716 exited, status 75
Aug 23 17:37:50 localhost master[3545]: service lmtpunix pid 16716 in READY state: terminated abnormally

 

Solution:

# service cyrus-imapd stop
# rm /var/lib/imap/tls_sessions.db*
# rm /var/lib/imap/deliver.db*
# rm /var/lib/imap/db/*
# service cyrus-imapd start

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Posted by on 23 Ağustos 2014 in Bilgisayar, Linux, Server

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1 dk’da Bulut Sunucu

Aşağıda linki bulunan DigitalOcean Adlı servisten 1 dk’da istediğiniz konfigürasyonda hazır LAMP vb. kurulmuş bulut sunucu oluşturabilirsiniz. Üstelik ücretlendirme saat bazlı. Sildiğiniz sunucunun imajı oluşuyor ve kullanmadığınız için para ödemiyorsunuz.

https://www.digitalocean.com/

 

 

Posted by on 18 Ağustos 2014 in Bilgisayar, Linux, Programlama

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Unzip: skipping filename.zip need PK compat. v4.6 (can do v2.1)

Sometimes extracting a zip file using the unzip command may result in the “skipping: filename.zip  need PK compat. v4.5″ error message.

# unzip filename.zip
Archive:  filename.zip
   skipping: filename.zip  need PK compat. v4.6 (can do v2.1)

This is due to the file been compressed with the latest version of PKZIP which the unzip command cannot handle. The solution is to install p7zip package which can handle the files compressed using PKZIP.

Download the latest version of p7zip:

# wget http://downloads.sourceforge.net/project/p7zip/p7zip/9.20.1/p7zip_9.20.1_x86_linux_bin.tar.bz2?r=http%3A%2F%2Fsourceforge.net%2Fprojects%2Fp7zip%2Ffiles%2Fp7zip%2F9.20.1%2Fp7zip_9.20.1_x86_linux_bin.tar.bz2%2Fdownload&ts=1390605043&use_mirror=garr

Extract the file

# tar -jxf p7zip_9.20.1_x86_linux_bin.tar.bz2

goto the extracted directory and run the installer

# ./install.sh

This will install the ’7za’ command on your server using which the zip file can be extracted

# 7za x filename.zip
 Processing archive: filename.zip
 Extracting  filename
 Everything is Ok

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Posted by on 25 Ocak 2014 in Bilgisayar, Linux, Server

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