How can a large file, say 1GB, for some testing purposes be created?

Solution :

Use the following command :

dd if=/dev/zero of= filename bs=1024 count=1024number of 0′s

Replace ‘filename’ with the actual filename.
Replace ‘number of 0′s’ with the required number of 0′s

For example,
One ’0′ for 10MB , two for 100 MB and so on..

For the above scenario (file of size 1GB), use the following command :

dd if=/dev/zero of=file.test bs=1024 count=1024000

There is no control panel installed on the server. So, how can the total number of user accounts on the system be determined?

Solution:

Use the following command to find the total number of accounts on the system :

cat /etc/passwd | wc -l

Note : This will also include system accounts like root, mail etc.

To list all the accounts on the system then use the following :

cat /etc/passwd | cut -d”:” -f1

How can a particular email account be ‘disabled’ temporarily. Note that the email account should not be ‘deleted’ ? Is this possible at all via cPanel?

Solution :

There is no direct functionality in cPanel at the moment for this. This feature might be added at a later stage.
However, you can achieve this functionality by modifying a few entries via SSH.

Comment out the entries related to the particular email account in the following locations:
/home/user/etc/domainname/passwd
/home/user/etc/domainname/shadow
/home/user/etc/domainname/quota

Make sure that you just comment them and NOT delete them as you might need them back later.

Need to transfer a folder from a remote server to the local server.

Solution :

One way of doing this is using the ‘wget’ command.

First, log in to your server via SSH and and launch wget mirroring using the following command :

wget -m ftp://username:password@ftp.host/folder/

Do replace the above with the corresponding values.

This will mirror the folder to your current directory location.

Finally, copy the downloaded files from the ftp.host/ directory to where you need them to be.

The main advantage of this method is that it is much more interactive and has many options.
Use ‘wget –help’ or ‘man wget’ for more information on this.

Source : WHT

SFTP users can view server files and folders by simply changing the path to ‘/’. How can this be avoided?

Solution :

SFTP means FTP access over SSH.
You will have to chroot the individual users in order to prevent them from viewing files outside their chroot jail.
Normal FTP access has chroot isolation at the ftp daemon level.

How to find files containing a specific word and store the results in another text file ?

Solution :

Use the following command :

grep -R word /directory/* > filename

Use -iR instead of -R for case insensitive search.
This approach will take some time depending on the size and number of files.

A faster method is to use the locate command.

First run the following command to create/update the search database:

updatedb

Then run the following command :

locate string > results.txt

Here are some steps to reset the permissions.

/scripts/checkbsdgroups — Checks and repairs proftpd ownership on FreeBSD.
/scripts/chownpublichtmls — Change ownership of all users web space to them, which is useful for converting to suexec. Files owned by nobody are deleted.

Then, login to WHM as ‘root’ and go to Whm >> Resellers >> Reseller Center >> Reset Resellers

Select all Resellers under Reset package permissions to default and click the reset button.

Assuming that you have an ACL with the default permissions, select all Resellers under ‘Apply an ACL list to multiple resellers >> Select the appropriate ACL list >> Apply.

Also, it is advised to run the following :

/scripts/fixeverything/
/scripts/upcp –force

service httpd restart
service named restart

Also, refer to Changing multiple account ownerships via SSH

How to change the default port for SSH?

Solution :

Open the port (which you want to use for SSH) in the server firewall and restart the firewall to apply the change.
Then, open the configuration file /etc/ssh/sshd_config using your favorite editor and change :

#Port 22
to
Port x

Replace ‘x’ with the required port number.

Restart sshd :

/etc/init.d/sshd restart

How to change the IPs of multiple accounts on a server in one go? The option in WHM is tedious. Hence, it does not serve the purpose.

Solution :

You need to have ‘root’ SSH access in order to do this.
Create a file and put the concerned accounts in it in the following format:

domainname1: user1
domainname2: user2
and so on..

Now execute the following command :

for i in `cat /path/to/file | cut -d: -f1`
do
/usr/local/cpanel/bin/swapip OLDIP NEWIP $i;
done;

Replace OLDIP and NEWIP with the corresponding values.

When you create a sub-domain, cPanel points it to the corresponding folder under public_html by default. How to point it to a folder outside the public_html?

Solution :

This cannot be done via cPanel/WHM but can be achieved if you have ‘root’ SSH access to the server.

1. Open the apache configuration file — /usr/local/apache/conf/httpd.conf
2. Search for the virtual host entry for your sub-domain.
3. Edit the document root of your sub-domain to match the desired location.
4. Save and Exit. Restart apache.

Note : cPanel rebuilds httpd.conf from userdata files and its overwritten on every cPanel update, on every account creation, subdomain addition, or any such activity related to apache and any manual changes you make will be overwritten. To make permanent changes to a subdomain’s root folder :

1. Edit the file /var/cpanel/userdata/username/subdomain.domain.com file, change the path and save it.
2. Run /scripts/rebuildhttpdconf
3. Restart apache.

To learn how you can preserve the changes in httpd.conf during EasyApache, click here.

The SSH connection times out on few minutes of inactivity.

Fix :

Most likely, you are using SSH protocol 2 .
To get around the above problem, you can simply increase the ClientAliveInterval in the file /etc/ssh/sshd_config to (say) 300 seconds.

After allocating jailshell , the user is not able to use commands like ‘ls’ , ‘touch’ , ‘mkdir’ etc. within his own home directory.

Fix:

Try the following steps :

1. Get into the directory /home/virtfs/username/home/ via SSH and check the ownership and permissions of the folder named username inside this directory. The ownership should be username.username and permissions should be 711 .

2. If the above does not work then try un-mounting the entire virtfs directory and log back in to the SSH user:

root@server [~]# umount /home/virtfs//home//

How to check successful and failed SSH logins to the server ?

Solution :

Use the following commands (as root) to achieve this :

last | less

This captures data from /var/log/wtmp and shows you the successful logins.

lastb | less

This captures data from /var/log/btmp and shows you the failed attempts.

Source : WHT

How to go about setting up backups using SSH so that backups of every account are uploaded automatically from server1 to server2 ?

Solution :

1. Make SSH password less (key based) from destination to source.

2. Run a rsync from destination to get files from source.

3. Set it as a cron every night according to the server load.

How to allow SFTP but disallow shell-level access ?

Solution :

To allow SFTP access but without shell access, you must first enable (jailed) shell via WHM. But then run the following so they do not have command line/shell access:

usermod -s /usr/local/cpanel/bin/noshell username

Of course, replace “username” with the actual account user name.

Then generate a key pair for the account in question:

cd /home/userid/.ssh

Run:
ssh-keygen
(Accept the default names, i.e. id_rsa)
Enter any passphrase and be sure to remember the passphrase used.

After this two files will be created:

id_rsa
***This is the private key.
id_rsa.pub
***This is the public key.

Now entering the following:

cat id_rsa.pub >> authorized_keys

The id_rsa file is the private key to be used with FileZilla:

Preferences —> SFTP —> add key file.

Then configure FileZilla with SFTP and port – (insert ssh access port here), the user ID but NO password.

Remove both files from the on-line account:
id_rsa.pub
id_rsa

Now SFTP transfers should work.