CentOS DHCP
Contents
Issue
On CentOS 7.x, if you have NetworkManager running and managing the NIC for dhcp address lease, you will not find the active lease in /var/lib/dhclient directory. The name of the currect lease file will be generated by NetworkManager with the interface name as part of the file name.
Client Lease file
On DHCP client machine running CentOS 7.x, when NetworkManager is enable, check the following directory for possible dhclient processor id:
cd /var/var ls -l | grep dhclient [root@localhost run]# ls -l | grep dhclient -rw-r--r--. 1 root root 5 Sep 22 03:41 dhclient-enp0s25.pid
"cat" the file "dhclient-enp0s25.pid", this should be the process that obtains an IP address from the DHCP server:
[root@localhost run]# cat dhclient-enp0s25.pid 3707
Run the command "lsof -p 3707" to find out which files are opened by the this dhcp client process:
[root@localhost run]# lsof -p 3707
lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs
Output information may be incomplete.
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
dhclient 3707 root cwd DIR 253,1 4096 128 /
dhclient 3707 root rtd DIR 253,1 4096 128 /
dhclient 3707 root txt REG 253,1 424272 69175939 /usr/sbin/dhclient
dhclient 3707 root mem REG 253,1 61928 70044141 /usr/lib64/libnss_files-2.17.so
dhclient 3707 root mem REG 253,1 398264 69337527 /usr/lib64/libpcre.so.1.2.0
dhclient 3707 root mem REG 253,1 11376 67413136 /usr/lib64/libfreebl3.so
dhclient 3707 root mem REG 253,1 147120 67413192 /usr/lib64/libselinux.so.1
dhclient 3707 root mem REG 253,1 40816 70044128 /usr/lib64/libcrypt-2.17.so
dhclient 3707 root mem REG 253,1 68192 67413300 /usr/lib64/libbz2.so.1.0.6
dhclient 3707 root mem REG 253,1 91496 67882403 /usr/lib64/libelf-0.163.so
dhclient 3707 root mem REG 253,1 153192 67413288 /usr/lib64/liblzma.so.5.0.99
dhclient 3707 root mem REG 253,1 19888 67413799 /usr/lib64/libattr.so.1.1.0
dhclient 3707 root mem REG 253,1 15688 67413495 /usr/lib64/libkeyutils.so.1.5
dhclient 3707 root mem REG 253,1 62720 69337485 /usr/lib64/libkrb5support.so.0.1
dhclient 3707 root mem REG 253,1 251784 67109588 /usr/lib64/libnspr4.so
dhclient 3707 root mem REG 253,1 20016 69337487 /usr/lib64/libplc4.so
dhclient 3707 root mem REG 253,1 15768 69337497 /usr/lib64/libplds4.so
dhclient 3707 root mem REG 253,1 182056 69337496 /usr/lib64/libnssutil3.so
dhclient 3707 root mem REG 253,1 1220152 68189018 /usr/lib64/libnss3.so
dhclient 3707 root mem REG 253,1 164016 69261726 /usr/lib64/libsmime3.so
dhclient 3707 root mem REG 253,1 276688 69261727 /usr/lib64/libssl3.so
dhclient 3707 root mem REG 253,1 121296 67413483 /usr/lib64/libsasl2.so.3.0.0
dhclient 3707 root mem REG 253,1 110808 70044151 /usr/lib64/libresolv-2.17.so
dhclient 3707 root mem REG 253,1 88720 70044117 /usr/lib64/libgcc_s-4.8.5-20150702.so.1
dhclient 3707 root mem REG 253,1 297464 67882460 /usr/lib64/libdw-0.163.so
dhclient 3707 root mem REG 253,1 44096 70102429 /usr/lib64/librt-2.17.so
dhclient 3707 root mem REG 253,1 19520 70044130 /usr/lib64/libdl-2.17.so
dhclient 3707 root mem REG 253,1 1141560 70044133 /usr/lib64/libm-2.17.so
dhclient 3707 root mem REG 253,1 90632 67118658 /usr/lib64/libz.so.1.2.7
dhclient 3707 root mem REG 253,1 1509376 69337523 /usr/lib64/libxml2.so.2.9.1
dhclient 3707 root mem REG 253,1 142304 70044149 /usr/lib64/libpthread-2.17.so
dhclient 3707 root mem REG 253,1 20024 67413801 /usr/lib64/libcap.so.2.22
dhclient 3707 root mem REG 253,1 2017168 69337492 /usr/lib64/libcrypto.so.1.0.1e
dhclient 3707 root mem REG 253,1 15840 67413200 /usr/lib64/libcom_err.so.2.1
dhclient 3707 root mem REG 253,1 202576 69337473 /usr/lib64/libk5crypto.so.3.1
dhclient 3707 root mem REG 253,1 950496 69337483 /usr/lib64/libkrb5.so.3.3
dhclient 3707 root mem REG 253,1 316528 67413306 /usr/lib64/libgssapi_krb5.so.2.2
dhclient 3707 root mem REG 253,1 2112384 69450411 /usr/lib64/libc-2.17.so
dhclient 3707 root mem REG 253,1 344248 69634318 /usr/lib64/libldap-2.4.so.2.10.3
dhclient 3707 root mem REG 253,1 61856 69634316 /usr/lib64/liblber-2.4.so.2.10.3
dhclient 3707 root mem REG 253,1 23968 67413490 /usr/lib64/libcap-ng.so.0.0.0
dhclient 3707 root mem REG 253,1 365352 70591020 /usr/lib64/libisc-export.so.95.2.1
dhclient 3707 root mem REG 253,1 1332264 70591016 /usr/lib64/libdns-export.so.100.1.1
dhclient 3707 root mem REG 253,1 125216 68981254 /usr/lib64/libomapi.so.0.0.0
dhclient 3707 root mem REG 253,1 164440 67413121 /usr/lib64/ld-2.17.so
dhclient 3707 root mem REG 253,1 26272 69759965 /usr/lib64/libsystemd-daemon.so.0.0.12
dhclient 3707 root 0r CHR 1,3 0t0 1039 /dev/null
dhclient 3707 root 1w CHR 1,3 0t0 1039 /dev/null
dhclient 3707 root 2w CHR 1,3 0t0 1039 /dev/null
dhclient 3707 root 3u unix 0xffff8800af3c8400 0t0 36030 socket
dhclient 3707 root 4w REG 253,1 766 137315992 /var/lib/NetworkManager/dhclient-8a2d820f-f6b9-4f5c-aaa4-edca33a393c6-enp0s25.lease
dhclient 3707 root 5u pack 36040 0t0 ALL type=SOCK_RAW
dhclient 3707 root 6u IPv4 35236 0t0 UDP *:bootpc
dhclient 3707 root 20u IPv4 36031 0t0 UDP *:9554
dhclient 3707 root 21u IPv6 36032 0t0 UDP *:wag-service
Check the directory for the normal location for dhcp lease file store by the client:
[root@localhost dhclient]# ls -l /var/lib/dhclient total 0
Please note that it is empty. From the above "lsof" output, check the /var/lib/NetworkManager directory contents:
[root@localhost dhclient]# ls /var/lib/NetworkManager/ dhclient-06a501aa-fed4-47fb-a470-5e215e9422de-virbr1-nic.lease dhclient-24e40adc-e339-4588-ad56-9f94a5e966fe-virbr1-nic.lease dhclient-47329694-77a8-4337-a638-fededd6e104d-virbr0-nic.lease dhclient-5eb6278c-3bfc-4662-9e81-1b5b29194905-virbr1-nic.lease dhclient-6c1bac15-9650-4853-8a7e-6fbf294a60e7-virbr1-nic.lease dhclient-7932d78b-9d43-485b-8046-c4293b7c3cce-virbr0-nic.lease dhclient-8a2d820f-f6b9-4f5c-aaa4-edca33a393c6-enp0s25.lease dhclient-9772f47f-c9f5-4939-b835-a4b647d224c5-virbr0-nic.lease dhclient-ae8067cc-c66d-4451-aad2-6313c46bc806-virbr0-nic.lease dhclient-aecbf20b-3cda-4f8d-bcef-0d22fa57dd57-virbr1-nic.lease dhclient-b9f35cbd-ba0c-492d-acc1-79581e614ffb-virbr0-nic.lease dhclient-d36d3082-4bf2-4fa5-b911-79217a88dd16-virbr1-nic.lease dhclient-eb416a23-ce17-41f3-9920-00ac6e677c4c-virbr0-nic.lease dhclient-ed73d158-b707-460c-bae1-6dd8dd779f5b-virbr0-nic.lease dhclient-enp0s25.conf dhclient-f97cd8eb-1567-4f5d-8405-dac75a296bff-vnet1.lease NetworkManager.state timestamps timestamps.DR4IOY
Check the contents of dhclient-8a2d820f-f6b9-4f5c-aaa4-edca33a393c6-enp0s25.lease. Note the time date and time are UTC time.
[root@localhost dhclient]# cat /var/lib/NetworkManager/dhclient-8a2d820f-f6b9-4f5c-aaa4-edca33a393c6-enp0s25.lease
lease {
interface "enp0s25";
fixed-address 192.168.53.100;
option subnet-mask 255.255.255.0;
option dhcp-lease-time 4294967295;
option routers 192.168.53.1;
option dhcp-message-type 5;
option dhcp-server-identifier 192.168.53.1;
option domain-name-servers 192.168.53.1;
renew 1 2084/10/09 06:04:15;
rebind 2 2135/10/25 14:29:44;
expire 0 2152/10/29 09:18:22;
}
lease {
interface "enp0s25";
fixed-address 192.168.53.100;
option subnet-mask 255.255.255.0;
option routers 192.168.53.1;
option dhcp-lease-time 4294967295;
option dhcp-message-type 5;
option domain-name-servers 192.168.53.1;
option dhcp-server-identifier 192.168.53.1;
renew 2 2084/10/10 10:56:04;
rebind 2 2135/10/25 19:21:33;
expire 0 2152/10/29 14:10:11;
}
Information about the NIC enp0s25:
[root@localhost dhclient]# ifconfig enp0s25
enp0s25: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.53.100 netmask 255.255.255.0 broadcast 192.168.53.255
inet6 fe80::21c:c0ff:fea5:9b82 prefixlen 64 scopeid 0x20<link>
ether 00:1c:c0:a5:9b:82 txqueuelen 1000 (Ethernet)
RX packets 22382 bytes 20488641 (19.5 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 17934 bytes 3642148 (3.4 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device interrupt 20 memory 0xe0200000-e0220000
Please note that in the above case, the DHCP server has been configured to reserve 192.168.53.100 for DHCP client with MAC address 00:1c:c0:a5:9b:82
Reference
DHCP relasted RFCs
- RFC1541
- RFC2131
- RFC2132
