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Description of problem: for following /etc/dhcp/dhclient-exit-hooks causes some strange behavior with DHCP on AWS. #!/bin/bash OPTIONS="options timeout:1 attempts:1" if grep -Fxq "$OPTIONS" /etc/resolv.conf then exit else echo "; generated by /etc/dhcp/dhclient-exit-hooks" >> /etc/resolv.conf echo ${OPTIONS} >> /etc/resolv.conf fi [root@piwik-prod-076 centos]# > /etc/resolv.conf [root@piwik-prod-076 centos]# tail -f /etc/resolv.conf ; generated by /etc/dhcp/dhclient-exit-hooks options timeout:1 attempts:1 tail: /etc/resolv.conf: file truncated options timeout:1 attempts:1 In the end we just have an /etc/resolv.conf with "options timeout:1 attempts:1". It is very strange as the comment line "; generated by /etc/dhcp/dhclient-exit-hooks" gets written and then, as we can see with the above output, gets truncated. Version-Release number of selected component (if applicable): CentOS Linux release 7.1.1503 (Core) on AWS How reproducible: Easily reproducible with our env Steps to Reproduce: 1. Set up dhclient-exit-hooks with the above 2. $> /etc/resolv.conf 3 $tail -F on /etc/resolv.conf 3. systemctl network restart on another terminal. Actual results: [root@piwik-prod-076 centos]# cat /etc/resolv.conf options timeout:1 attempts:1 <extra line> Expected results: ; generated by /etc/dhcp/dhclient-exit-hooks options timeout:1 attempts:1 search cloud.foo.com nameserver 1.2.3.4 nameserver 1.2.3.4 Additional info: Using a custom dotp from AWS with two name servers and a search domain. [root@piwik-prod-076 centos]# tcpdump -i eth0 port 67 or port 68 -e -n -vvv tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 10:55:36.212268 02:32:0d:4e:ce:2f > Broadcast, ethertype IPv4 (0x0800), length 342: (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 328) 0.0.0.0.bootpc > 255.255.255.255.bootps: [udp sum ok] BOOTP/DHCP, Request from 02:32:0d:4e:ce:2f, length 300, xid 0xb9586021, Flags [none] (0x0000) Client-Ethernet-Address 02:32:0d:4e:ce:2f Vendor-rfc1048 Extensions Magic Cookie 0x63825363 DHCP-Message Option 53, length 1: Request Requested-IP Option 50, length 4: 10.141.5.132 Parameter-Request Option 55, length 13: Subnet-Mask, BR, Time-Zone, Classless-Static-Route Domain-Name, Domain-Name-Server, Hostname, YD YS, NTP, MTU, Option 119 Default-Gateway END Option 255, length 0 PAD Option 0, length 0, occurs 35 10:55:36.212767 02:85:83:3b:2a:47 > 02:32:0d:4e:ce:2f, ethertype IPv4 (0x0800), length 363: (tos 0x10, ttl 16, id 0, offset 0, flags [none], proto UDP (17), length 349) 10.141.5.1.bootps > 10.141.5.132.bootpc: [udp sum ok] BOOTP/DHCP, Reply, length 321, xid 0xb9586021, Flags [none] (0x0000) Your-IP 10.141.5.132 Client-Ethernet-Address 02:32:0d:4e:ce:2f Vendor-rfc1048 Extensions Magic Cookie 0x63825363 DHCP-Message Option 53, length 1: ACK Server-ID Option 54, length 4: 10.141.5.1 Lease-Time Option 51, length 4: 3600 Subnet-Mask Option 1, length 4: 255.255.255.0 BR Option 28, length 4: 10.141.5.255 Domain-Name Option 15, length 14: "cloud.dcmn.com" Domain-Name-Server Option 6, length 8: 10.141.10.231,10.141.9.153 Hostname Option 12, length 15: "ip-10-141-5-132" MTU Option 26, length 2: 9001 Default-Gateway Option 3, length 4: 10.141.5.1 END Option 255, length 0