Crontab in Linux - Mithun Technologies - +91-9980923226
Mithun Technologies +91-9980923226 devopstrainingblr@gmail.com
http://mithuntechnologies.com/
http://mithuntechnologies.co.in/
Crontab
To allow or deny access to specific users, crontab uses the files /etc/cron.allow and /etc/cron.deny. Based on the existence of /etc/cron.allow and /etc/cron.deny files, crontab decides whom to give access to cron in following order.
- If cron.allow exists – only the users listed in the file cron.allow will get an access to crontab.
- If cron.allow does not exist – all users except the users listed into cron.deny can use crontab
- If neither of the file exists – only the root can use crontab
- If a user is listed in both cron.allow and cron.deny – that user can use crontab.
crontab -l : To display the cron jobs.
crontab -e : To edit the cron table.
crontab -r : To remove the crontable without confirmation.
crontab -ir: To remove the crontable with confirmation.
To list,schedule or remove cron job for the particular user, use below commands.
#crontab -l -u mithun
#crontab -e -u mithun
#crontab -ir -u mithun
Crontab Format
# Minute Hour Day of Month Month Day of Week Command /Script
# (0-59) (0-23) (1-31) (1-12 or Jan-Dec) (0-6 or Sun-Sat) /usr/bin/find
Run the cron job every minute.
*/1 * * * *
Run the cron job every 10 minutes.
*/10 * * * *
crontab -e : To edit the cron table.
crontab -r : To remove the crontable without confirmation.
crontab -ir: To remove the crontable with confirmation.
To list,schedule or remove cron job for the particular user, use below commands.
#crontab -l -u mithun
#crontab -e -u mithun
#crontab -ir -u mithun
Crontab Format
# Minute Hour Day of Month Month Day of Week Command /Script
# (0-59) (0-23) (1-31) (1-12 or Jan-Dec) (0-6 or Sun-Sat) /usr/bin/find
Run the cron job every minute.
*/1 * * * *
Run the cron job every 10 minutes.
*/10 * * * *
Saturday, February 22, 2020
Steps to create password less ssh between two AWS EC2 instances - Mithun Technologues - +91-9980923226
Steps to create password less ssh between two AWS EC2 instances - Mithun Technologies - 9980923226
Mithun Technologies +91-9980923226 devopstrainingblr@gmail.com
http://mithuntechnologies.com/
http://mithuntechnologies.co.in/
Steps to create password less ssh between two AWS EC2 instances
Pre Requisites
2 Linux Servers
Redhat Linux Server - A
IP: 13.233.128.180
User: ec2-user
Password: ********
Redhat Linux Server - B
IP: 13.127.64.6
User: ec2-user
Password: ********
Step 1
Generate the ssh key using below command in Redhat Linux Server - A
ssh-keygey
~/.ssh/
id_rsa
id_rsa.pub
Step 2
Copy the public key from Redhat Linux Server - A to Redhat Linux Server - B as follows.
ssh-copy-id ec-user@Redhat Linux Server - B HostName/IP Address
Step 3
Test the configurations as follows.
ssh ec2-user@Redhat Linux Server - B HostName/IP Address
It should not ask the password and It will successfully connected to Redhat Linux Server - B from Redhat Linux Server - A
Tuesday, October 22, 2019
AWS Password Login - Configuration - Mithun Technologies +91-9980923226
Mithun Technologies +91-9980923226 devopstrainingblr@gmail.com
http://mithuntechnologies.com/http://mithuntechnologies.co.in/
Enable a password login instead of pem file when logging into EC2 Instance using SSH
================================================================
Procedure to Enable the password login
---------------------------------------------------
Step 1) First login into ec2 instance with pem file, then switch to root user.
ssh -i "mithuntechnologies.pem" ec2-user@ec2-52-66-196-244.ap-south-1.compute.amazonaws.com
sudo su - (OR) sudo -i
Step 2) Set a password for ec2-user as follows.
passwd ec2-user
Step 3) Update the PasswordAuthentication parameter in the /etc/ssh/sshd_config file as follows.
vi /etc/ssh/sshd_config
PasswordAuthentication yes
Step 4) Restart the sshd service as follows.
service sshd restart
Nexus Server Installation in Linux - Mithun Technologies - +91-9980923226
Mithun Technologies +91-9980923226 devopstrainingblr@gmail.com
http://mithuntechnologies.com/http://mithuntechnologies.co.in/
Login as a root user
sudo su -
cd /opt
yum install tar wget -y
wget http://download.sonatype.com/nexus/3/nexus-3.15.2-01-unix.tar.gz
tar -zxvf nexus-3.15.2-01-unix.tar.gz
mv /opt/nexus-3.15.2-01 /opt/nexus
#As a good security practice, Nexus is not advised to run nexus service as a root user, so create a new user called nexus and grant sudo access to manage nexus services as follows.
useradd nexus
#Give the sudo access to nexus user
visudo
nexus ALL=(ALL) NOPASSWD: ALL
#Change the owner and group permissions to /opt/nexus and /opt/sonatype-work directories.
chown -R nexus:nexus /opt/nexus
chown -R nexus:nexus /opt/sonatype-work
chmod -R 775 /opt/nexus
chmod -R 775 /opt/sonatype-work
#Open /opt/nexus/bin/nexus.rc file and uncomment run_as_user parameter and set as nexus user.
vi /opt/nexus/bin/nexus.rc
run_as_user="nexus"
#Create nexus as a service
ln -s /opt/nexus/bin/nexus /etc/init.d/nexus
#Switch as a nexus user and start the nexus service as follows.
sudo su - nexus
#Enable the nexus services
sudo systemctl enable nexus
#Start the nexus service
sudo systemctl start nexus
#Access the Nexus server from Laptop/Desktop browser.
http://IPAddess/Hostname:8081/
#Default Credentials
User Name:
Password:
Troubleshooting
---------------------
nexus service is not starting?
a)make sure need to change the ownership and group to /opt/nexus and /opt/sonatype-work directories and permissions (775) for nexus user.
b)make sure you are trying to start nexus service with nexus user.
c)check java is installed or not using java -version command.
d) check the nexus.log file which is availabe in /opt/sonatype-work/nexus3/log directory.
Unable to access nexus URL?
-------------------------------------
a)make sure port 8081 is opened in security groups in AWS ec2 instance.
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