I've got a small problem changing the IP of my Raspberry (Raspian Stretch lite) via PHP.

I wrote a small php page to modify the IP-Address setting by reading a template file replacing the blanks and writing it to /etc/dhcpcd.conf. I gave the webserver user (www-data) the permission to write the file and it all works as intended.

After the next boot the server can't find any configuration and set the IP address of the Raspberry to the default DHCP without reaching server address (169.254.X.X).

When I open the file (/etc/dhcpcd.conf) now with sudo nano /etc/dhcpcd.conf save it (CTRL + o) and exit (CTRL + x) it without changing anything and reboot afterwards it gets the correct IP address.

The rewritten file looks like this:

# A sample configuration for dhcpcd.
# See dhcpcd.conf(5) for details.

# Allow users of this group to interact with dhcpcd via the control socket.
#controlgroup wheel

# Inform the DHCP server of our hostname for DDNS.

# Use the hardware address of the interface for the Client ID.
# or
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 ClientID as per RFC4361.
# Some non-RFC compliant DHCP servers do not reply with this set.
# In this case, comment out duid and enable clientid above.

# Persist interface configuration when dhcpcd exits.

# Rapid commit support.
# Safe to enable by default because it requires the equivalent option set
# on the server to actually work.
option rapid_commit

# A list of options to request from the DHCP server.
option domain_name_servers, domain_name, domain_search, host_name
option classless_static_routes
# Most distributions have NTP support.
option ntp_servers
# Respect the network MTU. This is applied to DHCP routes.
option interface_mtu

# A ServerID is required by RFC2131.
require dhcp_server_identifier

# Generate Stable Private IPv6 Addresses instead of hardware based ones
slaac private

# Example static IP configuration:
interface eth0
static ip_address=
#static ip6_address=fd51:42f8:caae:d92e::ff/64
#static routers=
#static domain_name_servers= fd51:42f8:caae:d92e::1

# It is possible to fall back to a static IP if DHCP fails:
# define static profile
#profile static_eth0
#static ip_address=
#static routers=
#static domain_name_servers=

# fallback to static profile on eth0
#interface eth0
#fallback static_eth0
  • You said, "After the next boot the server can't find any configuration and set the IP-Address of the raspberry to the default dhcp without reaching server address (169.254.X.X)." What server? Your question seems to be missing some information.
    – Seamus
    Commented Jul 9, 2018 at 11:56
  • oups sry i meant the "raspberry" not server.
    – Nik
    Commented Jul 9, 2018 at 12:17
  • 1
    I'm voting to close this question as off-topic because the actual issue (invisible characters in the config file) is likely not relevant to anybody except the OP. Commented Jul 9, 2018 at 12:44

1 Answer 1


I just resolved the Problem. Here's the description if anybody with a similar problem found this question.

There were some non visible chars in the template file.

I detected them with the command "cat -A {Template_File}". after opening and closing the file with nano they were gone and my php site work as intended now :)

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