Daily tasks automation : low memory

Email notification if memory is low

subject="Server Memory Status Alert"
##sending mail as
from="server.monitor@example.com"
## sending mail to
to="admin1@example.com"
## send carbon copy to
also_to="admin2@example.com"

## get total free memory size in megabytes(MB) 
free=$(free -mt | grep Total | awk '{print $4}')
## check if free memory is less or equals to  100MB
if [[ "$free" -le 100  ]]; then
## get top processes consuming system memory and save to temporary file 
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head >/tmp/top_proccesses_consuming_memory.txt
file=/tmp/top_proccesses_consuming_memory.txt
## send email if system memory is running low
echo -e "Warning, server memory is running low!\n\nFree memory: $free MB" | mailx -a "$file" -s "$subject" -r "$from" -c "$to" "$also_to"
fi
exit 0

Daily Task Automation : Read the logs and notify

Below script will continuously read the log and will trigger an email if it founds a match for the string

#!/bin/bash

string=fail

while true
do
if tail -f /path/to/file | grep $string
then
echo -e "String found on $HOSTNAME" | mail -s "Subject" dummy@iam.com
fi
done

Installing GUI in AWS EC2 - RHEL7

There are three sections involved in the whole setup. Follow all the three sections explained below to successfully configure the GUI.

sudo yum -y update
Install the gnome GUI components using the following command.
sudo yum groupinstall -y "Server with GUI"
Issue the following commands to start the GUI during boot.

sudo systemctl set-default graphical.target

sudo systemctl default

Now we have all the essential GUI components installed on the server. In the next section, we will install the xrdp components to enable remote desktop connections.

Setting Up XRDP

Add the xrdp repository to your instance using the following command.

sudo rpm -Uvh http://li.nux.ro/download/nux/dextop/el7/x86_64/nux-dextop-release-0-1.el7.nux.noarch.rpm

Install xrdp and tiger VNC server.

sudo yum install -y xrdp tigervnc-server

Setup SELINUX security using the following commands.

chcon --type=bin_t /usr/sbin/xrdp

chcon --type=bin_t /usr/sbin/xrdp-sesman

Start and enable the xrdp service.

1 2	sudo systemctl start xrdp sudo systemctl enable xrdp

Enable RDP port on the instance using the following firewall commands.

sudo firewall-cmd --permanent --add-port=3389/tcp

sudo firewall-cmd --reload

Set a password for ec2-user . This password will be used to connect to the RDP session.

sudo passwd ec2-user

Set password for root as you will be prompted for cloud user password for network proxy and color. Login as root and set the password.

1 2	sudo su passwd

Now we have the xdrp components and all instance level settings in the right place. Now let’s test out the RDP connection from an RDP client. In this tutorial, i am using windows RDP client.

Connecting The Instance Using RDP

Note: Make sure you have opened RDP port in your instance security group.

1. Open RDP client and type in the public IP of your instance and click connect.

2. If you get a warning message about remote identity, just click yes.

3. Now you will get a xrdp authentication window, enter the credentials and click ok.

Note: The username is “ec2-user” and the password is the password you set for ec2-user in step 6.

4. You will be prompted to enter the password again. Provide the password and proceed to the steps to configure the initial desktop.

5. If it prompts for “cloud user password” provide the root user password you set in step 7.

6. That it, you will get a GUI session as shown below. If you face any errors do let me know in the comment session.

Source : https://devopscube.com/how-to-setup-gui-for-amazon-ec2-rhel-7-instance/

What is the use of enumerate function in python

enumerate() is one of the built-in Python functions. It returns an enumerate object. In our case that object is a list of tuples (immutable lists), each containing a pair of count/index and value. 

>>> choices = ['pizza', 'pasta', 'salad', 'nachos']
>>> list(enumerate(choices))
=> [(0, 'pizza'), (1, 'pasta'), (2, 'salad'), (3, 'nachos')]

So, in the for index, item in enumerate(choices): expressionindex, item is the pair of count, value of each tuple: (0, 'pizza'), (1, 'pasta'), ...

We may easily change the start count/index with help ofenumerate(sequence, start=0)
for index, item in enumerate(choices, start = 1):
    print index, item


or simply with a number as the second parameter
for index, item in enumerate(choices, 1):
    print index, item
Try the following code:


>>>with open ('/etc/passwd') as f1:

...    ab = f1.readlines()

...     for i,v in enumerate(ab, 1):        

...      print i,v

File handling in Python Cheatsheet: All modes

• r

  Opens a file for reading only. The file pointer is placed at the beginning of the file. This is the default mode.

• rb

  Opens a file for reading only in binary format. The file pointer is placed at the beginning of the file. This is the default mode.

• r+

  Opens a file for both reading and writing. The file pointer will be at the beginning of the file. 

  (cannot truncate a file)

• rb+

  Opens a file for both reading and writing in binary format. The file pointer will be at the beginning of the file.

• w

  Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.

• wb

  Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.

• w+

  Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.

  (can truncate a file)

• wb+

  Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.

• a

  Opens a file for appending. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing.

• ab 

  Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing.

• a+

  Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.

• ab+

  Opens a file for both appending and reading in binary format. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.

Important

Always make sure you explicitly close each open file, once its job is done and you have no reason to keep it open. Because - There is an upper limit to the number of files a program can open. If you exceed that limit, there is no reliable way of recovery, so the program could crash. - Each open file consumes some main-memory for the data-structures associated with it, like file descriptor/handle or file locks etc. So you could essentially end-up wasting lots of memory if you have more files open that are not useful or usable. - Open files always stand a chance of corruption and data loss.

Unable to connect to RHN network - ping works but nslookup fails

You should have proper entries in /etc/hosts and /etc/nsswitch.conf

Usually, you'll want its hosts line to look like(in /etc/nsswitch.conf):

hosts:      files dns

Antoher file to check is /etc/resolv.conf
check the permissions of all these files.

Read: http://superuser.com/questions/704785/ping-cant-resolve-hostname-but-nslookup-can

Installing Python modules using pip

pip is a package management system used to install and manage software packages written in Python. Many packages can be found in the Python Package Index (PyPI). Python 2.7.9 and later (on the python2 series), and Python 3.4 and later include pip (pip3 forPython 3) by default.

Install steps: https://pip.pypa.io/en/stable/installing/

Wget https://bootstrap.pypa.io/get-pip.py

Then run the following:

python get-pip.py

Install paramiko using pip

For reference, paramiko which we install has a hard dependency on cryptography which states:

For Debian and Ubuntu, the following command will ensure that the required dependencies are installed:

$ sudo apt-get install build-essential libssl-dev libffi-dev python-dev

For Fedora and RHEL-derivatives, the following command will ensure that the required dependencies are installed:

$ sudo yum install gcc libffi-devel python-devel openssl-devel

#pip install paramiko