>>
>> Any help modifying the above recipe or pointer to how to do it these
>> days would be appreciated.
>
>
> I just declare the root file system as read-only in fstab and create
> some
> ramdisks for stuff that needs to be writable.
>
> LABEL=rootfs / ext4 ro,noatime,errors=remount-ro 0 1
> debugfs /sys/kernel/debug debugfs defaults 0 0
> tmpfs /var/log tmpfs defaults,noatime,nosuid,mode=0777,size=128M 0
> 0
> tmpfs /var/tmp tmpfs defaults,noatime,nosuid,size=16M 0 0
> tmpfs /tmp tmpfs defaults,noatime,nosuid,size=128M 0 0
>
> Service generic-board-startup (a.k.a.
> /opt/scripts/boot/generic-startup.sh)
> must run once with a writable root to set up a bunch of stuff (on later
> boots it complains, but it doesn't seem to matter). After that you're
> stuck
> hacking all the software which expects to be able to write to disk. For
> a
> working network, "/etc/resolv.conf" needs symlinking to a writable
> location.
> Many services expect to persistently store their stuff under "/var/lib".
>
> I've used tmpfiles.d to create required symlinks, e.g.
>
> $ cat /etc/tmpfiles.d/10-ro-symlinks.conf
> L+ /etc/resolv.conf - - - - /var/run/symlinks/etc/resolv.conf
> L+ /etc/ppp/resolv.conf - - - - /var/run/symlinks/etc/ppp/resolv.conf
Hmm having tried this I don't get it. This fragment seem to be assuming
that:
* the dirs /var/run/symlinks/etc etc. are created somehow, maybe
with a d line in the same file?
* the link target files /var/run/symlinks/etc/resolv.conf exist,
I guess they can just be empty as connection manager is going to fix
them up for me anyway?
Thanks,
Britton
Right. I wanted to emphasize only the important lines, but prerequisites are
important too 
Here's the full file
#Type Path Mode UID GID Age Argument
d /var/run/symlinks 0755 - - -
d /var/run/symlinks/etc 0755 - - -
d /var/run/symlinks/etc/ppp 0755 - - -
f /var/run/symlinks/etc/resolv.conf 0755 - - -
f /var/run/symlinks/etc/ppp/resolv.conf 0755 - - -
# NB! Connman might override this by linking
"/usr/lib/tmpfiles.d/connman_resolvconf.conf" to "/run/connman/resolv.conf"
L+ /etc/resolv.conf - - - - /var/run/symlinks/etc/resolv.conf
L+ /etc/ppp/resolv.conf - - - - /var/run/symlinks/etc/ppp/resolv.conf
Ok this work, thanks so much. There are still a couple things I don't
get though:
* I notice in your original replay you don't have a tmpfs for /run
(which is sym linked to from /var/run). So I wonder how the dirs
and files you create from /etc/tmpfiles.d/10-ro-symlinks.conf are
getting created, since I would think they would be on the (read-only)
root file system. Is there something missing from the fstab you
originally showed? I included this line as well:
tmpfs /run tmpfs defaults,noatime,nosuid,size=16M 0 0
I haven't gone back and tested without it, so maybe it works as you
show and I just don't understand how.
* I end up with a rw tmpfs for /root (root home dir), as shown by
cat /etc/mtab (last line):
root@bbone217slave:/etc# cat /etc/mtab
sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
udev /dev devtmpfs rw,relatime,size=10240k,nr_inodes=55575,mode=755 0 0
devpts /dev/pts devpts
rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /run tmpfs rw,nosuid,noatime,size=16384k,mode=755 0 0
/dev/mmcblk1p1 / ext4 ro,noatime,errors=remount-ro,data=ordered 0 0
securityfs /sys/kernel/security securityfs
rw,nosuid,nodev,noexec,relatime 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
tmpfs /run/lock tmpfs rw,nosuid,nodev,noexec,relatime,size=5120k 0 0
tmpfs /sys/fs/cgroup tmpfs ro,nosuid,nodev,noexec,mode=755 0 0
cgroup /sys/fs/cgroup/systemd cgroup
rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd
0 0
cgroup /sys/fs/cgroup/blkio cgroup rw,nosuid,nodev,noexec,relatime,blkio 0 0
cgroup /sys/fs/cgroup/net_cls,net_prio cgroup
rw,nosuid,nodev,noexec,relatime,net_cls,net_prio 0 0
cgroup /sys/fs/cgroup/devices cgroup
rw,nosuid,nodev,noexec,relatime,devices 0 0
cgroup /sys/fs/cgroup/cpuset cgroup
rw,nosuid,nodev,noexec,relatime,cpuset 0 0
cgroup /sys/fs/cgroup/cpu,cpuacct cgroup
rw,nosuid,nodev,noexec,relatime,cpu,cpuacct 0 0
cgroup /sys/fs/cgroup/perf_event cgroup
rw,nosuid,nodev,noexec,relatime,perf_event 0 0
cgroup /sys/fs/cgroup/pids cgroup rw,nosuid,nodev,noexec,relatime,pids 0 0
cgroup /sys/fs/cgroup/freezer cgroup
rw,nosuid,nodev,noexec,relatime,freezer 0 0
cgroup /sys/fs/cgroup/memory cgroup
rw,nosuid,nodev,noexec,relatime,memory 0 0
systemd-1 /proc/sys/fs/binfmt_misc autofs
rw,relatime,fd=30,pgrp=1,timeout=0,minproto=5,maxproto=5,direct 0 0
mqueue /dev/mqueue mqueue rw,relatime 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
fusectl /sys/fs/fuse/connections fusectl rw,relatime 0 0
configfs /sys/kernel/config configfs rw,relatime 0 0
tmpfs /var/log tmpfs rw,nosuid,noatime,size=131072k,mode=777 0 0
tmpfs /var/tmp tmpfs rw,nosuid,noatime,size=16384k 0 0
tmpfs /tmp tmpfs rw,nosuid,noatime,size=131072k 0 0
tmpfs /root tmpfs rw,relatime 0 0
I don't know what mechanism causes this? It presumably is why my old
way of doing this once worked.
Britton
