Difference between passwd and passwd- file as well as shadow and shadow- file

Question

on my server running UnraidOS I got a bit suspicious. There are both 'passwd' and 'passwd-' files (same goes for shadow(-)). These ones should be only backups as I understood.

Running:

root@Unraid-server:~# diff /etc/passwd{,-}

delivers:

2,8c2,8
< bin:x:1:1:bin:/bin:/bin/false
< daemon:x:2:2:daemon:/sbin:/bin/false
< adm:x:3:4:adm:/var/log:/bin/false
< ftp:x:14:50::/home/ftp:/bin/false
< rpc:x:32:32:RPC portmap user:/:/bin/false
< sshd:x:33:33:sshd:/:/bin/false
< ntp:x:44:44:User for NTP:/:/bin/false
---
> bin:!:1:1:bin:/bin:/bin/false
> daemon:!:2:2:daemon:/sbin:/bin/false
> adm:!:3:4:adm:/var/log:/bin/false
> ftp:!:14:50::/home/ftp:/bin/false
> rpc:!:32:32:RPC portmap user:/:/bin/false
> sshd:!:33:33:sshd:/:/bin/false
> ntp:!:44:44:User for NTP:/:/bin/false
10,14c10,14
< dhcpcd:x:68:68:dhcp PrivSep:/var/lib/dhcpcd:/bin/false
< avahi:x:61:214:Avahi Daemon User:/dev/null:/bin/false
< avahi-autoipd:x:62:62:Avahi AutoIP Daemon User:/dev/null:/bin/false
< messagebus:x:81:81:User for D-BUS:/var/run/dbus:/bin/false
< nobody:x:99:100:nobody:/:/bin/false
---
> dhcpcd:!:68:68:dhcp PrivSep:/var/lib/dhcpcd:/bin/false
> avahi:!:61:214:Avahi Daemon User:/dev/null:/bin/false
> avahi-autoipd:!:62:62:Avahi AutoIP Daemon User:/dev/null:/bin/false
> messagebus:!:81:81:User for D-BUS:/var/run/dbus:/bin/false
> nobody:!:99:100:nobody:/:/bin/false

As it seems, only all the 'x' for '!' were changed in the back-uped version. Nothing changed here in terms of the user id, just the 'locked' status was applied.

A) This is correct and not suspicious, right?

For shadow it is a bit different:

root@Unraid-server:~# diff /etc/shadow{,-}
2,11c2,11
< bin:!:19469:0:99999:7:::
< daemon:!:19469:0:99999:7:::
< adm:!:19469:0:99999:7:::
< ftp:!:19469:0:99999:7:::
< rpc:!:19469:0:99999:7:::
< sshd:!:19469:0:99999:7:::
< avahi:!:19469:0:99999:7:::
< avahi-autoipd:!:19469:0:99999:7:::
< messagebus:!:19469:0:99999:7:::
< nobody:!:19469:0:99999:7:::
---
> bin:!:19451:0:99999:7:::
> daemon:!:19451:0:99999:7:::
> adm:!:19451:0:99999:7:::
> ftp:!:19451:0:99999:7:::
> rpc:!:19451:0:99999:7:::
> sshd:!:19451:0:99999:7:::
> avahi:!:19451:0:99999:7:::
> avahi-autoipd:!:19451:0:99999:7:::
> messagebus:!:19451:0:99999:7:::
> nobody:!:19451:0:99999:7:::
15c15
< ntp:!:19469::::::
---
> ntp:!:19451::::::
17c17
< dhcpcd:!:19469::::::
---
> dhcpcd:!:19451::::::

Shouldn't there be the same user-id on shadow as well as shadow-? Why are the user-id's changed between the original file and the backup? -> on my /boot/config file the user-id of original shadow file are equivalent.

Answer 1

The filenames with a dash in the end are backup files which are created automatically wherever you add/alter/remove users or groups.

Shouldn't there be the same user-id on shadow as well as shadow-?

No. This is not an ID but the date of the most recent change (encoded as the number of days since Jan 1, 1970). See also the shadow(5) manual (man shadow).