DHCP Leases in Linux: Management, Commands & Troubleshooting

dhcp leases are temporary IP address assignments from a DHCP server to clients, recorded in lease files. Managed via systemd-networkd, dhclient, or ISC DHCP on Linux.

# View server lease database (systemd-networkd acting as server)
cat /var/lib/systemd/lease/*.lease

Overview

DHCP leases track which IP address, subnet mask, gateway, and lease duration have been assigned to each client. Leases expire unless renewed. Administrators inspect leases to resolve IP conflicts, audit active clients, or verify static reservations. On Linux, the storage location and query tools differ by DHCP implementation.

dhcp leases Syntax Reference

DHCP lease management does not have a single dhcp leases binary. Inspect and manipulate leases using these commands across different implementations.

# systemd-networkd – view active client leases
cat /run/systemd/netif/leases/*

# systemd-networkd – view server lease database (acting as DHCP server)
cat /var/lib/systemd/lease/*.lease

# dhclient – view client leases (ISC DHCP client)
cat /var/lib/dhcp/dhclient.leases

# ISC DHCP server – query active leases
sudo dhcp-lease-list
less /var/lib/dhcp/dhcpd.leases

# Force release/renew with dhclient
sudo dhclient -r eth0
sudo dhclient eth0

# systemd-networkd – restart to reload leases
sudo systemctl restart systemd-networkd

# Logs for DHCP events
journalctl -u systemd-networkd --no-pager | grep -i lease

dhcp leases Rapid Reference Cheat Sheet

Advanced Implementation & Parameters

systemd-networkd DHCP Server Lease Storage

When systemd-networkd acts as a DHCP server (configured via DHCPServer=yes in a .network file), leases are written to /var/lib/systemd/lease/. Each lease file is named by the client identifier (usually the MAC address) and contains JSON with assigned IP, lease time, and options.

# Inspect a server lease
cat /var/lib/systemd/lease/be:5e:56:66:75:16.lease

{
  "address": "192.168.223.225",
  "lease_time": 86400,
  "client_id": "01:be:5e:56:66:75:16",
  "gateway": "192.168.223.1",
  "subnet_mask": "255.255.255.240",
  "server_id": "192.168.223.1"
}

Static Leases in systemd-networkd

Static leases are defined in the [DHCPServerStaticLease] section of a .network file. The server must be configured with DHCPServer=yes and a pool address range (e.g., Pool=). The MAC address must match the client’s actual MAC.

[Match]
Name=ve-perft3

[Network]
DHCPServer=yes
Address=0.0.0.0/28

[DHCPServerStaticLease]
MACAddress=be:5e:56:66:75:16
Address=192.168.223.225

# Release current lease without stopping dhclient
sudo dhclient -r eth0
# Stop dhclient daemon and release lease
sudo dhclient -x eth0

# Display all active leases
sudo dhcp-lease-list
# Continuous refresh every 5 seconds
watch -n 5 sudo dhcp-lease-list

# Example: eth0 IP 192.168.1.10/24
subnet 192.168.1.0 netmask 255.255.255.0 {
}
# Then restart dhcpd
sudo systemctl restart isc-dhcp-server

# AWS: list all private IPs assigned via DHCP
aws ec2 describe-network-interfaces --query 'NetworkInterfaces[*].PrivateIpAddress'
# On Cisco IOS:
show ip dhcp binding

# Fast pipeline for active leases to CSV
sudo awk '/lease/{ip=$2} /starts/{s=$2 $3} /ends/{e=$2 $3; if(e >= systime()) print ip", "s", "e}' /var/lib/dhcp/dhcpd.leases > active_leases.csv
# Alternative with csvformat
sudo grep -B2 -A2 'binding state active' /var/lib/dhcp/dhcpd.leases | awk ... | csvformat -d ' '