No DHCPOFFERS received

why this  command not work?

freeartist@devuan:~$ sudo dhclient eth0
RTNETLINK answers: File exists
freeartist@devuan:~$ 

DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval

many times at booting and no network after booting

From a quick glance at that log file, it appears that dhcpcd is successfully obtaining a lease for 192.168.0.26 from a server at 192.168.0.1...
Then connman and networkmanager start fighting over the interface, killing each other's dhcpcd instances, and everything pretty much goes to hell.

Why exactly are you trying to use 3 different methods to configure your network all at the same time anyway? That's bound to cause chaos.

Pick one method to configure networking.
IIRC networkmanager will leave interfaces configured in /etc/network/interfaces alone by default, so ifup and networkmanager should be able to coexist peacefully... At least in theory.
That would still be confusing though, if you want to use networkmanager and have the interface come up before anyone logs in, look for a "system connection" or "available to all users" option in your networkmanager frontend of choice.

Otherwise, get rid of networkmanager and connman (as well as any other random actors you didn't mention) and just use /etc/network/interfaces like the good-old-days before all this overcomplicated gui crap came along.

steve@damnation:~$ crystal-ball --query "what did he do?"
crystal-ball: command not found

Oops, guess I misplaced it.

You can use a static IP address instead, that doesn't require a running dhcp daemon or DHCP router support. Just make sure you don't pick an address that's already in use.

DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval

many times at booting and no network after booting

I entered "dhclient syslog DHCPDISCOVER" into a search engine and found this:

https://serverfault.com/questions/32715 … r-of-times

If an NIC is configured in /etc/network/interfaces then NetworkManager will ignore it.

I always remove NM. It's useless bloat IMO.

DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval

many times at booting and no network after booting
syslog https://filebin.net/xlouztkn3ufvuos8

/etc/network/interfaces                                                                                                                                             

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

PS how can i choose networking? from upper config file or NetworkManager?

/etc/resolv.conf                                                                                                                                                  
nameserver 192.168.0.1
nameserver 185.253.74.33
nameserver 185.253.74.34

/etc/resolvconf.conf                                                                                                                                              
resolvconf=NO