Le fichier /var/lib/dhcp/dhclient.leases existe chez moi, mais il est vide (Ubuntu 16.04 avec NetworkManager).
Voici un exemple avec un PC portable, dont le nom est "vivien5", connecté en WiFi avec une Bbox ADSL :
$ ps auxww | grep -- "-lf .*\.lease" | grep -v grep | grep -v sed | sed 's{^.*-lf \(.*\.lease\).*{\1{'
/var/lib/NetworkManager/dhclient-5023463e-1415-4f67-997a-54518e51a2bf-wlp2s0.lease
On a plus que le bail DHCP en cours de validité :
$ cat /var/lib/NetworkManager/dhclient-5023463e-1415-4f67-997a-54518e51a2bf-wlp2s0.lease
lease {
interface "wlp2s0";
fixed-address 192.168.1.43;
option subnet-mask 255.255.255.0;
option dhcp-lease-time 86400;
option routers 192.168.1.254;
option dhcp-message-type 5;
option dhcp-server-identifier 192.168.1.254;
option domain-name-servers 192.168.1.254;
option interface-mtu 1500;
option dhcp-renewal-time 43200;
option dhcp-rebinding-time 75600;
option broadcast-address 192.168.1.255;
option host-name "vivien5-001";
option domain-name "lan";
renew 3 2016/07/20 07:47:12;
rebind 3 2016/07/20 17:50:16;
expire 3 2016/07/20 20:50:16;
}
lease {
interface "wlp2s0";
fixed-address 192.168.1.43;
option subnet-mask 255.255.255.0;
option routers 192.168.1.254;
option dhcp-lease-time 86400;
option dhcp-message-type 5;
option domain-name-servers 192.168.1.254;
option dhcp-server-identifier 192.168.1.254;
option interface-mtu 1500;
option dhcp-renewal-time 43200;
option broadcast-address 192.168.1.255;
option dhcp-rebinding-time 75600;
option host-name "vivien5-001";
option domain-name "lan";
renew 3 2016/07/20 13:37:48;
rebind 4 2016/07/21 01:01:27;
expire 4 2016/07/21 04:01:27;
}