1. Testing restart on package upgrade
$ lxc launch ubuntu:lunar l --vm
$ lxc shell l
# pidof multipathd
136
# echo "deb http://archive.ubuntu.com/ubuntu $(lsb_release -cs)-proposed restricted main multiverse universe" | sudo tee /etc/apt/sources.list.d/ubuntu-$(lsb_release -cs)-proposed.list
$ apt update -y && apt install -y multipath-tools -t $(lsb_release -cs)-proposed
<cut here>
Preparing to unpack .../kpartx_0.8.8-1ubuntu2.2_amd64.deb ...
Unpacking kpartx (0.8.8-1ubuntu2.2) over (0.8.8-1ubuntu2) ...
Preparing to unpack .../multipath-tools_0.8.8-1ubuntu2.2_amd64.deb ...
Unpacking multipath-tools (0.8.8-1ubuntu2.2) over (0.8.8-1ubuntu2) ...
Setting up kpartx (0.8.8-1ubuntu2.2) ...
Setting up multipath-tools (0.8.8-1ubuntu2.2) ...
The warning about having to reload systemd units can be safely ignored. Please see LP: #2035098 for detail
s.
Warning: The unit file, source configuration file or drop-ins of multipathd.service changed on disk. Run '
systemctl daemon-reload' to reload units.
Could not execute systemctl:  at /usr/bin/deb-systemd-invoke line 145.
Removing obsolete conffile /etc/init.d/multipath-tools ...
Processing triggers for man-db (2.11.2-1) ...
Processing triggers for libc-bin (2.37-0ubuntu2.1) ...
< cut here>
# pidof multipathd
1622
# systemctl status multipathd.{service,socket} | grep Active -B2
● multipathd.service - Device-Mapper Multipath Device Controller
     Loaded: loaded (/lib/systemd/system/multipathd.service; enabled; preset: enabled)
     Active: active (running) since Mon 2023-10-16 15:51:49 UTC; 36s ago
--
○ multipathd.socket - multipathd control socket
     Loaded: loaded (/lib/systemd/system/multipathd.socket; enabled; preset: enabled)
     Active: inactive (dead) since Mon 2023-10-16 15:51:47 UTC; 37s ago




2. Downgrading
# apt install -y multipath-tools=0.8.8-1ubuntu2 --allow-downgrades
# pidof multipathd
1866
# systemctl status multipathd.{service,socket} | grep Active -B2
● multipathd.service - Device-Mapper Multipath Device Controller
     Loaded: loaded (/lib/systemd/system/multipathd.service; enabled; preset: enabled)
     Active: active (running) since Mon 2023-10-16 15:52:57 UTC; 13s ago
--
● multipathd.socket - multipathd control socket
     Loaded: loaded (/lib/systemd/system/multipathd.socket; enabled; preset: enabled)
     Active: active (running) since Mon 2023-10-16 15:52:57 UTC; 13s ago




3. Installing a fresh package (no warning message here because dpkg is lt-nl)
# apt purge multipath-tools -y
# apt install -y multipath-tools -t $(lsb_release -cs)-proposed
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Suggested packages:
  multipath-tools-boot
The following NEW packages will be installed:
  multipath-tools
0 upgraded, 1 newly installed, 0 to remove and 40 not upgraded.
Need to get 328 kB of archives.
After this operation, 1231 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu lunar-proposed/main amd64 multipath-tools amd64 0.8.8-1ubuntu2.2 [328 kB]
Fetched 328 kB in 1s (588 kB/s)     
Selecting previously unselected package multipath-tools.
(Reading database ... 57514 files and directories currently installed.)
Preparing to unpack .../multipath-tools_0.8.8-1ubuntu2.2_amd64.deb ...
Unpacking multipath-tools (0.8.8-1ubuntu2.2) ...
Setting up multipath-tools (0.8.8-1ubuntu2.2) ...
Created symlink /etc/systemd/system/multipath-tools.service → /lib/systemd/system/multipathd.service.
Created symlink /etc/systemd/system/sysinit.target.wants/multipathd.service → /lib/systemd/system/multipat
hd.service.
Created symlink /etc/systemd/system/sockets.target.wants/multipathd.socket → /lib/systemd/system/multipath
d.socket.
Could not execute systemctl:  at /usr/bin/deb-systemd-invoke line 145.
Processing triggers for man-db (2.11.2-1) ...
Processing triggers for libc-bin (2.37-0ubuntu2.1) ...
Scanning processes...                                                                                     
Scanning linux images...                                                                                  

Running kernel seems to be up-to-date.

No services need to be restarted.

No containers need to be restarted.

No user sessions are running outdated binaries.

No VM guests are running outdated hypervisor (qemu) binaries on this host.

# systemctl status multipathd.{service,socket} | grep Active -B2
● multipathd.service - Device-Mapper Multipath Device Controller
     Loaded: loaded (/lib/systemd/system/multipathd.service; enabled; preset: enabled)
     Active: active (running) since Mon 2023-10-16 15:54:03 UTC; 35s ago
--
○ multipathd.socket - multipathd control socket
     Loaded: loaded (/lib/systemd/system/multipathd.socket; enabled; preset: enabled)
     Active: inactive (dead)




4. Upgrading to a future package
# wget https://launchpad.net/ubuntu/+archive/primary/+files/kpartx_0.8.8-1ubuntu2.2_amd64.deb
# wget https://launchpad.net/ubuntu/+archive/primary/+files/multipath-tools_0.8.8-1ubuntu2.2_amd64.deb
# mkdir tmp
# dpkg-deb -R multipath-tools_0.8.8-1ubuntu2.2_amd64.deb tmp/
# sed -i s/1ubuntu2.2/1ubuntu2.3/g tmp/DEBIAN/control
# dpkg-deb -b tmp/ mpath2.3.deb
# mkdir kpartxtmp
# dpkg-deb -R kpartx_0.8.8-1ubuntu2.2_amd64.deb kpartxtmp/
# sed -i s/1ubuntu2.2/1ubuntu2.3/g kpartxtmp/DEBIAN/control
# dpkg-deb -b kpartxtmp/ kpartx2.3.deb
# dpkg -i kpartx2.3.deb
# dpkg -i mpath2.3.deb
# dpkg -l multipath-tools | grep multipath-tools | awk '{print $3}'
0.8.8-1ubuntu2.3
# systemctl status multipathd.{service,socket} | grep Active -B2
● multipathd.service - Device-Mapper Multipath Device Controller
     Loaded: loaded (/lib/systemd/system/multipathd.service; enabled; preset: enabled)
     Active: active (running) since Mon 2023-10-16 15:59:08 UTC; 11s ago
--
○ multipathd.socket - multipathd control socket
     Loaded: loaded (/lib/systemd/system/multipathd.socket; enabled; preset: enabled)
     Active: inactive (dead)



5. Testing multipath-tools functionality after upgading from current main
# apt purge multipath-tools kpartx
# apt install -y multipath-tools=0.8.8-1ubuntu2
# apt install -y lsscsi open-iscsi tgt
# dpkg -l multipath-tools | grep multipath-tools | awk '{print $3}'
0.8.8-1ubuntu2

Copy the following lines to a script called “setup.sh” anywhere
```
targetname="iqn.2016-11.foo.com:target.iscsi"
cwd=$(pwd)
testdir="/mnt/tgtmpathtest"
localhost="127.0.0.1"
portal="${localhost}:3260"
maxpaths=4
backfn="backingfile"
expectwwid="60000000000000000e00000000010001"
testdisk="/dev/disk/by-id/wwn-0x${expectwwid}"
### Setup mpath devices
# Restart tgtd to make sure modules are all loaded
service tgt restart || echo "Failed to restart tgt" >&2
# prep SINGLE test file
truncate --size 100M ${backfn}
# create target
tgtadm --lld iscsi --op new --mode target --tid 1 -T "${targetname}"
# allow all to bind the target
tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
# set backing file
tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b "${cwd}/${backfn}"
# scan for targets (locally)
iscsiadm --mode discovery --type sendtargets --portal ${localhost}
# login
echo "login #1"
iscsiadm --mode node --targetname "${targetname}" --portal ${portal} --login
# duplicate this session (always 1)
for i in $(seq 2 ${maxpaths})
do
    echo "extra login #${i}"
    iscsiadm --mode session -r 1 --op new
done
udevadm settle
sleep 5 # sleep a bit to allow device to be created.
# status summary
echo "Status after initial setup"
tgtadm --lld iscsi --mode target --op show
tgtadm --lld iscsi --op show --mode conn --tid 1
iscsiadm --mode session -P 1
lsscsi -liv
multipath -v3 -ll
dmsetup table
echo "Test WWN should now point to DM"
readlink "${testdisk}" | grep dm
```
# chmod +x setup.sh
# ./setup.sh
# multipath -ll
mpatha (360000000000000000e00000000010001) dm-0 IET,VIRTUAL-DISK
size=100M features='0' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=1 status=active
| `- 9:0:0:1  sdd 8:48 active ready running
|-+- policy='service-time 0' prio=1 status=enabled
| `- 7:0:0:1  sdb 8:16 active ready running
|-+- policy='service-time 0' prio=1 status=enabled
| `- 8:0:0:1  sdc 8:32 active ready running
`-+- policy='service-time 0' prio=1 status=enabled
  `- 10:0:0:1 sde 8:64 active ready running
# lsblk
NAME     MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
loop0      7:0    0  73.9M  1 loop  /snap/core22/864
loop1      7:1    0 180.9M  1 loop  /snap/lxd/25846
loop2      7:2    0  40.8M  1 loop  /snap/snapd/20092
sda        8:0    0    10G  0 disk  
├─sda1     8:1    0   9.9G  0 part  /
├─sda14    8:14   0     4M  0 part  
└─sda15    8:15   0   106M  0 part  /boot/efi
sdb        8:16   0   100M  0 disk  
└─mpatha 253:0    0   100M  0s mpath 
sdc        8:32   0   100M  0 disk  
└─mpatha 253:0    0   100M  0 mpath 
sdd        8:48   0   100M  0 disk  
└─mpatha 253:0    0   100M  0 mpath 
sde        8:64   0   100M  0 disk  
└─mpatha 253:0    0   100M  0 mpath 
# apt install -y multipath-tools -t $(lsb_release -cs)-proposed
# dpkg -l multipath-tools | grep multipath-tools | awk '{print $3}'
0.8.8-1ubuntu2.2
# multipath -ll
mpatha (360000000000000000e00000000010001) dm-0 IET,VIRTUAL-DISK
size=100M features='0' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=1 status=active
| `- 9:0:0:1  sdd 8:48 active ready running
|-+- policy='service-time 0' prio=1 status=enabled
| `- 7:0:0:1  sdb 8:16 active ready running
|-+- policy='service-time 0' prio=1 status=enabled
| `- 8:0:0:1  sdc 8:32 active ready running
`-+- policy='service-time 0' prio=1 status=enabled
  `- 10:0:0:1 sde 8:64 active ready running
root@j:~# lsblk
NAME     MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
loop0      7:0    0  73.9M  1 loop  /snap/core22/864
loop1      7:1    0 180.9M  1 loop  /snap/lxd/25846
loop2      7:2    0  40.8M  1 loop  /snap/snapd/20092
sda        8:0    0    10G  0 disk  
├─sda1     8:1    0   9.9G  0 part  /
├─sda14    8:14   0     4M  0 part  
└─sda15    8:15   0   106M  0 part  /boot/efi
sdb        8:16   0   100M  0 disk  
└─mpatha 253:0    0   100M  0 mpath 
sdc        8:32   0   100M  0 disk  
└─mpatha 253:0    0   100M  0 mpath 
sdd        8:48   0   100M  0 disk  
└─mpatha 253:0    0   100M  0 mpath 
sde        8:64   0   100M  0 disk  
└─mpatha 253:0    0   100M  0 mpath