Bashmagic collection vol1

Keep only last X lines of a file (shrink).

echo "$(tail -n 10000 huge.log)" > huge.log

Deploy maven artefact to a specific repo without specifying it in pom.xml (format repoId:default:repoUrl). Repo should be specified in your .m2 settings.xml with any necessary credentials.

mvn deploy -DaltDeploymentRepository=repo.mydomain.com.my.releases::default::https://repo.mydomain.com/repository/maven-my-releases/

One liner to set password for default PostgreSQL user after initial install.

runuser -l postgres -c $'psql -c "ALTER USER postgres WITH PASSWORD \'postgres\';"'

Run command inside a screen and save all output to a file

screen -dm bash -c 'script -c "some chatty command" output.txt'

Scroll around inside a screen.

screen -r myscreen

ctrl+a

[

ctrl+u and ctrl+d for up and down. bufer is limited

Add 4GB swap on Centos 7 with a stroke of a copy-paste.

sudo dd if=/dev/zero of=/swapfile count=4096 bs=1MiB
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Standard tcpdump.

tcpdump -i eth0 -s 65535 -w dump.pcap

Show listening ports with corresponding executables.

netstat -tulpn

Show systemd logs for a specific service.

journalctl -u nginx.service

Freshly installed nginx configured as reverse proxy on Centos 7 getting “Permission denied” when connecting to backend service

setsebool -P httpd_can_network_connect 1

Convert a certificate stored in a Java keystore to a PEM cert and key (for example, Tomcat to Nginx transition).

$JAVA_HOME/bin/keytool -importkeystore -srckeystore .keystore -destkeystore keystore.p12 -deststoretype PKCS12 -srcalias mycrtalias -deststorepass changeit -destkeypass changeit
openssl pkcs12 -in keystore.p12 -nokeys -out cert.pem
openssl pkcs12 -in keystore.p12 -nodes -nocerts -out key.pem

Disable git SSL verification per-repo.

git config http.sslVerify "false"

Disable git SSL verification at clone time.

git -c http.sslVerify=false clone something

Clear git username and password cache for a repo (in case of password change or similar).

git config --global --unset user.password

Give user sudo privileges.

sudo usermod -aG wheel <user>

Git submodule is added to an existing repo and is not resolving for you locally.

git submodule update --init --recursive

Print all TCP connections of a Docker container.

sudo docker inspect -f '{{.State.Pid}}' containerName
<result>
sudo nsenter -t <result> -n netstat

Nmap portscan.

sudo nmap -p 1-65535 -sV -sS -T4 <ip>

Force JVM to use /dev/urandom instead of /dev/random (sometimes needed in low entropy environments like Docker).

java -Djava.security.egd=file:/dev/./urandom ...

Debug print all network activities on JVM level.

java -Djavax.net.debug=all ...

Create .htpasswd file for Nginx

sudo sh -c "echo -n 'someuser:' >> /etc/nginx/.htpasswd"
sudo sh -c "openssl passwd -apr1 >> /etc/nginx/.htpasswd"

Do or do not do something if file was modified recently

RECENTLY_CHANGED=$(find /tmp/me -newermt '10 minutes ago' |wc -l |xargs)
if [ "$RECENTLY_CHANGED" -eq 1 ]; then
    echo "File was changed recently, terminating script"
    exit 0
fi

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