How do I show active dhcp leases
Try checking the lease file /var/lib/dhcp/dhcpd.leases
Our organization uses a Python script, as posted below, to examine the /var/lib/dhcp/dhcpd.leases file:
#!/usr/bin/python
import datetime, bisect
def parse_timestamp(raw_str):
tokens = raw_str.split()
if len(tokens) == 1:
if tokens[0].lower() == 'never':
return 'never';
else:
raise Exception('Parse error in timestamp')
elif len(tokens) == 3:
return datetime.datetime.strptime(' '.join(tokens[1:]),
'%Y/%m/%d %H:%M:%S')
else:
raise Exception('Parse error in timestamp')
def timestamp_is_ge(t1, t2):
if t1 == 'never':
return True
elif t2 == 'never':
return False
else:
return t1 >= t2
def timestamp_is_lt(t1, t2):
if t1 == 'never':
return False
elif t2 == 'never':
return t1 != 'never'
else:
return t1 < t2
def timestamp_is_between(t, tstart, tend):
return timestamp_is_ge(t, tstart) and timestamp_is_lt(t, tend)
def parse_hardware(raw_str):
tokens = raw_str.split()
if len(tokens) == 2:
return tokens[1]
else:
raise Exception('Parse error in hardware')
def strip_endquotes(raw_str):
return raw_str.strip('"')
def identity(raw_str):
return raw_str
def parse_binding_state(raw_str):
tokens = raw_str.split()
if len(tokens) == 2:
return tokens[1]
else:
raise Exception('Parse error in binding state')
def parse_next_binding_state(raw_str):
tokens = raw_str.split()
if len(tokens) == 3:
return tokens[2]
else:
raise Exception('Parse error in next binding state')
def parse_rewind_binding_state(raw_str):
tokens = raw_str.split()
if len(tokens) == 3:
return tokens[2]
else:
raise Exception('Parse error in next binding state')
def parse_leases_file(leases_file):
valid_keys = {
'starts': parse_timestamp,
'ends': parse_timestamp,
'tstp': parse_timestamp,
'tsfp': parse_timestamp,
'atsfp': parse_timestamp,
'cltt': parse_timestamp,
'hardware': parse_hardware,
'binding': parse_binding_state,
'next': parse_next_binding_state,
'rewind': parse_rewind_binding_state,
'uid': strip_endquotes,
'client-hostname': strip_endquotes,
'option': identity,
'set': identity,
'on': identity,
'abandoned': None,
'bootp': None,
'reserved': None,
}
leases_db = {}
lease_rec = {}
in_lease = False
in_failover = False
for line in leases_file:
if line.lstrip().startswith('#'):
continue
tokens = line.split()
if len(tokens) == 0:
continue
key = tokens[0].lower()
if key == 'lease':
if not in_lease:
ip_address = tokens[1]
lease_rec = {'ip_address' : ip_address}
in_lease = True
else:
raise Exception('Parse error in leases file')
elif key == 'failover':
in_failover = True
elif key == '}':
if in_lease:
for k in valid_keys:
if callable(valid_keys[k]):
lease_rec[k] = lease_rec.get(k, '')
else:
lease_rec[k] = False
ip_address = lease_rec['ip_address']
if ip_address in leases_db:
leases_db[ip_address].insert(0, lease_rec)
else:
leases_db[ip_address] = [lease_rec]
lease_rec = {}
in_lease = False
elif in_failover:
in_failover = False
continue
else:
raise Exception('Parse error in leases file')
elif key in valid_keys:
if in_lease:
value = line[(line.index(key) + len(key)):]
value = value.strip().rstrip(';').rstrip()
if callable(valid_keys[key]):
lease_rec[key] = valid_keys[key](value)
else:
lease_rec[key] = True
else:
raise Exception('Parse error in leases file')
else:
if in_lease:
raise Exception('Parse error in leases file')
if in_lease:
raise Exception('Parse error in leases file')
return leases_db
def round_timedelta(tdelta):
return datetime.timedelta(tdelta.days,
tdelta.seconds + (0 if tdelta.microseconds < 500000 else 1))
def timestamp_now():
n = datetime.datetime.utcnow()
return datetime.datetime(n.year, n.month, n.day, n.hour, n.minute,
n.second + (0 if n.microsecond < 500000 else 1))
def lease_is_active(lease_rec, as_of_ts):
return timestamp_is_between(as_of_ts, lease_rec['starts'],
lease_rec['ends'])
def ipv4_to_int(ipv4_addr):
parts = ipv4_addr.split('.')
return (int(parts[0]) << 24) + (int(parts[1]) << 16) + \
(int(parts[2]) << 8) + int(parts[3])
def select_active_leases(leases_db, as_of_ts):
retarray = []
sortedarray = []
for ip_address in leases_db:
lease_rec = leases_db[ip_address][0]
if lease_is_active(lease_rec, as_of_ts):
ip_as_int = ipv4_to_int(ip_address)
insertpos = bisect.bisect(sortedarray, ip_as_int)
sortedarray.insert(insertpos, ip_as_int)
retarray.insert(insertpos, lease_rec)
return retarray
##############################################################################
myfile = open('/var/lib/dhcp/dhcpd.leases', 'r')
leases = parse_leases_file(myfile)
myfile.close()
now = timestamp_now()
report_dataset = select_active_leases(leases, now)
print('+------------------------------------------------------------------------------')
print('| DHCPD ACTIVE LEASES REPORT')
print('+-----------------+-------------------+----------------------+-----------------')
print('| IP Address | MAC Address | Expires (days,H:M:S) | Client Hostname ')
print('+-----------------+-------------------+----------------------+-----------------')
for lease in report_dataset:
print('| ' + format(lease['ip_address'], '<15') + ' | ' + \
format(lease['hardware'], '<17') + ' | ' + \
format(str((lease['ends'] - now) if lease['ends'] != 'never' else 'never'), '>20') + ' | ' + \
lease['client-hostname'])
print('+-----------------+-------------------+----------------------+-----------------')
print('| Total Active Leases: ' + str(len(report_dataset)))
print('| Report generated (UTC): ' + str(now))
print('+------------------------------------------------------------------------------')
If you are using NetworkManager (which is default in many distributions) the .lease files is located in /var/lib/NetworkManager
$ sudo ls -al /var/lib/NetworkManager/*.lease
-rw-r--r-- 1 root root 399 Jun 12 10:23 /var/lib/NetworkManager/dhclient-6aef9d76-0f6a-46e3-8235-a4405a695b1a-eth0.lease
-rw-r--r-- 1 root root 856 Jun 12 10:30 /var/lib/NetworkManager/dhclient-86e97e19-0a11-4606-8edf-5a179ec6f82e-eth0.lease
-rw-r--r-- 1 root root 800 Jun 12 10:30 /var/lib/NetworkManager/dhclient-d0f4b29f-3059-4f55-a8d2-34db34310384-wlan0.lease
Here's a great command using CLI - You can go to the directory where dhcpd.log file is located and do:
tail -f dhcpd.log
That will show you leases as they are being issued by the server in real time.
You can also do:
cat /var/lib/dhcpd/dhcpd.leases to see leases that are in the lease file dhcpd.leases
Try enter this command:
dhcp-lease-list