here is the script. Tested working on Proxmox 8.4.x

#!/bin/bash
# Script to increase ulimits on a Proxmox VE 8.4 box
# Check if script is run as root
if [[ $EUID -ne 0 ]]; then
  echo "This script must be run as root. Exiting."
  exit 1
fi
# Define new ulimit values
NOFILE_SOFT=1048576
NOFILE_HARD=1048576
NPROC_SOFT=65536
NPROC_HARD=65536
echo "Increasing ulimits for open files and processes..."
# 1. Modify /etc/security/limits.conf
echo "Configuring /etc/security/limits.conf..."
cat << EOF >> /etc/security/limits.conf
# Added by increase_ulimits.sh
* soft nofile $NOFILE_SOFT
* hard nofile $NOFILE_HARD
* soft nproc $NPROC_SOFT
* hard nproc $NPROC_HARD
root soft nofile $NOFILE_SOFT
root hard nofile $NOFILE_HARD
root soft nproc $NPROC_SOFT
root hard nproc $NPROC_HARD
EOF
# 2. Modify /etc/systemd/system.conf
echo "Configuring /etc/systemd/system.conf..."
sed -i '/^#DefaultLimitNOFILE=/c\DefaultLimitNOFILE='$NOFILE_SOFT':'$NOFILE_HARD /etc/systemd/system.conf
sed -i '/^#DefaultLimitNPROC=/c\DefaultLimitNPROC='$NPROC_SOFT':'$NPROC_HARD /etc/systemd/system.conf
# 3. Modify /etc/systemd/user.conf
echo "Configuring /etc/systemd/user.conf..."
sed -i '/^#DefaultLimitNOFILE=/c\DefaultLimitNOFILE='$NOFILE_SOFT':'$NOFILE_HARD /etc/systemd/user.conf
sed -i '/^#DefaultLimitNPROC=/c\DefaultLimitNPROC='$NPROC_SOFT':'$NPROC_HARD /etc/systemd/user.conf
# 4. Update PAM configuration for login sessions
echo "Configuring PAM settings..."
cat << EOF >> /etc/pam.d/common-session
# Added by increase_ulimits.sh
session required pam_limits.so
EOF
cat << EOF >> /etc/pam.d/common-session-noninteractive
# Added by increase_ulimits.sh
session required pam_limits.so
EOF
# 5. Reload systemd daemon to apply changes
echo "Reloading systemd daemon..."
systemctl daemon-reload
# 6. Verify current ulimits for the root user
echo "Verifying ulimit settings for current session..."
su - root -c "ulimit -Sn && ulimit -Hn && ulimit -u"
echo "Note: Changes to session limits may require a reboot or relogin to take full effect."
# 7. Provide guidance for verification
echo "Ulimits configuration updated successfully."
echo "To verify after reboot, run: ulimit -n (for open files) and ulimit -u (for processes)."
echo "A system reboot is recommended to ensure all changes are applied."
exit 0