CentOS DHCP

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Issue

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 

[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

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