I have a script that checks a source folder for new files in case there are files in the source folder, it will move those files to destination.

The problem I encountered recently was that files are huge and it may be in the middle of the copying into source by another process so my script tries to move an incomplete file to a destination. Let's say the file is 4GB in size and just only 1GB of the file has been copied. I have to wait until file is 4GB and other handler using that file, then I should safely move the file.

You can use lsof command in order to check which processes are using the source file:

if [[ `lsof -- /var/my-folder/my-big-file.tar.gz` ]]
then
     echo "File is being used by a process."
     exit 1
 fi

NOTE: you can give file directly to lsof using -- or you can use grep command as follow:

lsof | grep /var/my-folder/my-big-file.tar.gz

NOTE2: if you are in a loop use break instead of exit.

NOTE3: if you get command not found, install it using apt-get install lsof

#linux #sysadmin #lsof #grep

How to limit bandwidth of rsync linux command?

rsync is an awesome tool in order to move files via ssh into another server or from server to local system like what scp does but
far better in terms of features and incremental copy mechanism. To limit bandwidth use bwlimit like below:

The general form:

rsync --bwlimit=<kb/second> <source> <dest>

An example of usage with 2MB limit per second transfer:

rsync --bwlimit=2000 /backup/folder user@example-host:/remote/backup/folder/

#linux #sysadmin #rsync #bandwidth

How to remove a user on CentOS 6?

userdel my-target-user

In case you want to remove all the associated user files too use -r parameter:

userdel -r my-target-user

Yes! As simple as that.

#linux #sysadmin #userdel #user #centos

https://xiaoxiaoke.wordpress.com/2015/10/06/changing-java-security-restriction-for-network-connect-error-issue-in-kvm/

#linux #devops #sysadmin #kvm #hp

How to SSH login without password?

You want to use Linux and OpenSSH to automate your tasks. Therefore you need an automatic login from host A / user a to Host B / user b. You don't want to enter any passwords, because you want to call ssh from a within a shell script.

How to do it?
First log in on A as user a and generate a pair of authentication keys. Do not enter a passphrase:

a@A:~> ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/a/.ssh/id_rsa):
Created directory '/home/a/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again: 
Your identification has been saved in /home/a/.ssh/id_rsa.
Your public key has been saved in /home/a/.ssh/id_rsa.pub.
The key fingerprint is:
3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 a@A

Now use ssh to create a directory ~/.ssh as user b on B. (The directory may already exist, which is fine):

a@A:~> ssh b@B mkdir -p .ssh
b@B's password:

Finally append a's new public key to b@B:.ssh/authorized_keys and enter b's password one last time:

a@A:~> cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys'
b@B's password:

From now on you can log into B as b from A as a without password:

a@A:~> ssh b@B

#linux #sysadmin #ssh #password_less #ssh_login

How to get default gateway IP address?

ip route | grep default

The output would be something like below:

default via 192.168.1.1 dev eth0 onlink

NOTE: it can be different on your system

#linux #sysadmin #ip #route #default_gateway

Virt-builder is a tool for quickly building new virtual machines. You can build a variety of VMs for local or cloud use, usually within a few minutes or less. Virt-builder also has many ways to customize these VMs. Everything is run from the command line and nothing requires root privileges, so automation and scripting is simple.

To see available virtual machines:

virt-builder --list

Sample command to create a debian-9 image:

sudo virt-builder debian-9 --size=50G --hostname prod.example.com --network --install network-manager --root-password password:YOUR_PASS

The above command creates a debian 9 image with disk size of 50GB and sets the hostname to prod.example.com. --network enables the networking on guest and --install installs packages on the target O
S. The last parameter sets the root password to YOUR_PASS.

To read more about the axtra parameters:
- http://libguestfs.org/virt-builder.1.html

#linux #sysadmin #virt_builder #debian #image

You can login to a server without entering a password by a simple command as below:

ssh-copy-id USERNAME@YOUR_HOST_IP -p 22

By issuing the above command it puts your public key content on server ~/.ssh/authorized_keys and prompts you to enter the password. You are all done by this.

#linux #sysadmin #ssh #passwordless_login #ssh_copy_id #authorized_keys #public_key

How I store & manage passwords in Linux for servers and other credentials? gopass

Password management should be simple and follow Unix philosophy. With pass, each secret lives inside of a gpg encrypted file whose filename is the title of the website or resource that requires the secret. These encrypted files may be organized into meaningful folder hierarchies, copied from computer to computer, and, in general, manipulated using standard command line file management utilities.

gopass is a rewrite of the pass password manager in Go with the aim of making it cross-platform and adding additional features. Our target audience are professional developers and sysadmins (and especially teams of those) who are well versed with a command line interface. One explicit goal for this project is to make it more approachable to non-technical users. We go by the UNIX philosophy and try to do one thing and do it well, providing a stellar user experience and a sane, simple interface:

- https://github.com/gopasspw/gopass

#unix #linux #sysadmin #pass #gopass #password_management #golang #github

https://stackoverflow.com/questions/13032409/ssh-remote-variable-assignment

#linux #sysadmin #ssh #local_variable #variable_expansion #bashrc #export

How to copy a file in the same path with a different name?

Well you just need to use curly braces, {}, to make it happen:

What you usually MIGHT do:

cp /usr/local/share/lib/sample.conf /usr/local/share/lib/settings.conf

You can take the smart path btw:

cp /usr/local/share/lib/{sample,settings}.conf

NOTE: if suffix of both files are different you can put that inside of curly braces too.

#linux #sysadmin #cp #copy #trick