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Old 4 Weeks Ago
mamalos mamalos is offline
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Default How to guarantee booting without manual intervention on an OpenBSD router

Hi everyone,

I have an OpenBSD 5.8 running on an alix apu1.d that operates as a router. Since this system is going to eventually be reset at some moment accidentally without properly unmounting its file systems, which means that, when booting, there is a possibility where automatic file system check won't be enough and fsck will have to run manually, I was wondering what the best way would be to manage such a situation.

At the moment, I thought of editing fstab to disable fsck for all file systems. The truth is that the only file systems that may be written when on operation is /var/log and /tmp (or /var/tmp as well), so boot wise I could just disable file system checks on these two file systems, but we'll discuss that if this solution is acceptable. So, is this method "safe" (since I don't care if I lose any newly written information in this machine) or will I end up with a non usable system? And if so, what would be the best solution that could allow for a system to "always" boot without leaving a chance of having to run fsck manually?

Thanks for your time and answers in advance!
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Old 4 Weeks Ago
J65nko J65nko is offline
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On booting, a memory/RAM file system for the writeable directories (mount_mfs(8)) will be newly (re)created/formatted.

mount_mfs is kind of an alias for newfs. They share so much functionality that they are the same binary and are described in the same man page.

Code:
$ ls -li /sbin/{newfs,mount_mfs} 
26020 -r-xr-xr-x  2 root  bin  214224 Dec 21  2012 /sbin/mount_mfs
26020 -r-xr-xr-x  2 root  bin  214224 Dec 21  2012 /sbin/newfs
These executables have the same inode, and one is thus a hard linked to the other.

From mount_mfs(8)
Code:
NAME
     newfs, mount_mfs - construct a new file system
With the -P option you specify a directory or file system that on (re)boot will be copied to the the newly newfsed file system.
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Last edited by J65nko; 4 Weeks Ago at 10:42 AM.
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mamalos mamalos is offline
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Thanks for the reply!

To see if I understood correctly, you're proposing me to replace /var and /tmp (and whichever writable file systems I "don't care about losing their data") in my fstab with a memory file system whose "source" will be the appropriate device node? If so, I like the idea, otherwise please re-explain.

Ah, and the -P option can be added in fstab's options?

EDIT: I am trying to create one but I don't think I'm getting the syntax right. I am not sure what to put as a special node (I tried md without luck). So I ran this:
Code:
# mount_mfs  -P /var -s 256m md /root/var
mount_mfs: md: No such file or directory
Could you please give an example (and also the relevant fstab entry)?

Last edited by mamalos; 4 Weeks Ago at 11:40 AM.
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Old 4 Weeks Ago
J65nko J65nko is offline
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What I am proposing is that you:
  • create a 'template' directory let us call it /Template
  • copy the /var contents to that directory, for example: # rsync -aviH /var/ /Template. Please note that the trailing "/" of /var/ is critical.

    EDIT: As pointed out by IdOp this is wrong, it should be:
    # rsync -aviH /var /Template


    You will now have a /Template/var with a clone of /var
  • create a directory for testing the mount: # mdir /monkey
  • edit your /etc/fstab to:
    Code:
    swap /monkey mfs rw,noexec,nosuid,-P=Template/var,s=80000 0 0
  • make an offering to Puffy and reboot
If I did not make a mistake you will now have the /var contents in /monkey.

I have to go out now, I could only test the rsync part ....
Good luck
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Last edited by J65nko; 4 Weeks Ago at 10:40 AM. Reason: Corrected according to IdOp's remark, and added '=" after -P option
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Quote:
Originally Posted by J65nko View Post
[*]copy the /var contents to that directory, for example: # rsync -aviH /var/ /Template. Please note that the trailing "/" of /var/ is critical.
You will now have a /Template/var with a clone of /var
I believe you want to leave the trailing '/' off of /var/ in the rsync command, otherwise you just get the contents of /var in the /Template directory, not /var itself as you want.
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J65nko J65nko is offline
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@ldOp, yes Your Honor, I plead guilty
Code:
$ sudo rsync -aviH -n  /var/ /Template/ | head -10 
sending incremental file list
.d..t...... ./
cd+++++++++ account/
cd+++++++++ audit/
cd+++++++++ authpf/
cd+++++++++ backups/
>f+++++++++ backups/device.backup
>f+++++++++ backups/device.current
>f+++++++++ backups/disklabel.sd0.backup
>f+++++++++ backups/disklabel.sd0.current
$ sudo rsync -aviH -n  /var/ /Template | head -10   
sending incremental file list
.d..t...... ./
cd+++++++++ account/
cd+++++++++ audit/
cd+++++++++ authpf/
cd+++++++++ backups/
>f+++++++++ backups/device.backup
>f+++++++++ backups/device.current
>f+++++++++ backups/disklabel.sd0.backup
>f+++++++++ backups/disklabel.sd0.current
As you stated correctly, /var without a trailing "/" works:
Code:
 $ sudo rsync -aviH -n  /var  /Template/ | head -10  
sending incremental file list
cd+++++++++ var/
cd+++++++++ var/account/
cd+++++++++ var/audit/
cd+++++++++ var/authpf/
cd+++++++++ var/backups/
>f+++++++++ var/backups/device.backup
>f+++++++++ var/backups/device.current
>f+++++++++ var/backups/disklabel.sd0.backup
>f+++++++++ var/backups/disklabel.sd0.current
According to the script(1) log this is also what I used.
My defense: "Significant other" was already complaining why I still was at the computer, when we were supposed to be leaving for Eindhoven ....

This also shows the importance of "peer review" , I suppose
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Old 4 Weeks Ago
J65nko J65nko is offline
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The following has been tested on an old OpenBSD machine:
Code:
# uname -a 
OpenBSD hercules.utp.xnet 5.2 GENERIC#9 amd64
So beware .
Code:
# ls -l /Template/var
total 92
drwxr-xr-x   2 root    wheel      512 Dec 21  2012 account
drwxrws---   2 root    wheel      512 Dec 21  2012 audit
drwxrwx---   2 root    authpf     512 Dec 21  2012 authpf
drwx------   2 root    wheel     6144 Jan 10 01:30 backups
drwxr-xr-x   3 root    wheel      512 Dec  4  2012 cache
drwxrwx---   2 root    wheel      512 Dec 26  2012 crash
dr-xr-xr-x   4 root    wheel      512 Jan 10 22:00 cron
drwxr-xr-x  10 root    wheel      512 Jan  9 03:30 db
drwxr-xr-x   3 root    wheel      512 Dec 21  2012 empty
drwxrwxr-x   5 root    games      512 Dec 26  2012 games
drwxr-xr-x   3 root    wheel     2048 Jan 10 22:00 log
drwxr-xr-x   2 root    wheel      512 Jan 10 01:30 mail
drwx------   8 _mysql  _mysql    2048 Aug 10 13:58 mysql
drwxr-xr-x   8 root    wheel      512 Dec 26  2012 named
drwxr-xr-x   6 root    wheel      512 Dec 21  2012 nsd
drwxr-x---   2 root    operator   512 Dec 21  2012 quotas
drwxr-xr-x   3 root    wheel      512 Jan 10 21:53 run
drwxr-xr-x   2 root    wheel      512 Dec 21  2012 rwho
drwxr-xr-x  11 root    wheel      512 Dec 31  2012 spool
drwxrwxrwt   3 root    wheel      512 Jan  9 03:30 tmp
drwxr-xr-x   2 root    wheel      512 Dec 21  2012 yp

# mount
/dev/wd0a on / type ffs (local, noatime, softdep)

# cat /etc/fstab
3a6d4322b09ba067.b none swap sw
3a6d4322b09ba067.a / ffs rw,noatime,softdep 1 1
swap               /monkey mfs rw,noatime,nosuid,noexec,-P=/Template/var,-s=120000

# mount
/dev/wd0a on / type ffs (local, noatime, softdep)

# swapctl -l
Device      512-blocks     Used    Avail Capacity  Priority
/dev/wd0b      4180991        0  4180991     0%    0

# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/wd0a     27.6G   15.0G   11.2G    57%    /

# mount -a
pax: /monkey/./cron/tabs/.sock skipped. Sockets cannot be copied or extracted
pax: /monkey/./empty/dev/log skipped. Sockets cannot be copied or extracted

# mount
/dev/wd0a on / type ffs (local, noatime, softdep)
mfs:5237 on /monkey type mfs (asynchronous, local, noatime, noexec, nosuid, size=120000 512-blocks)

# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/wd0a     27.6G   15.0G   11.2G    57%    /
mfs:5237      56.7M   38.1M   15.7M    71%    /monkey

# ls -l /monkey
total 56
drwxr-xr-x   2 root    wheel      512 Dec 21  2012 account
drwxrws---   2 root    wheel      512 Dec 21  2012 audit
drwxrwx---   2 root    authpf     512 Dec 21  2012 authpf
drwx------   2 root    wheel     6144 Jan 10 01:30 backups
drwxr-xr-x   3 root    wheel      512 Dec  4  2012 cache
drwxrwx---   2 root    wheel      512 Dec 26  2012 crash
dr-xr-xr-x   4 root    wheel      512 Jan 10 22:00 cron
drwxr-xr-x  10 root    wheel      512 Jan  9 03:30 db
drwxr-xr-x   3 root    wheel      512 Dec 21  2012 empty
drwxrwxr-x   5 root    games      512 Dec 26  2012 games
drwxr-xr-x   3 root    wheel     2048 Jan 10 22:00 log
drwxr-xr-x   2 root    wheel      512 Jan 10 01:30 mail
drwx------   8 _mysql  _mysql    2048 Aug 10 13:58 mysql
drwxr-xr-x   8 root    wheel      512 Dec 26  2012 named
drwxr-xr-x   6 root    wheel      512 Dec 21  2012 nsd
drwxr-x---   2 root    operator   512 Dec 21  2012 quotas
drwxr-xr-x   3 root    wheel      512 Jan 10 21:53 run
drwxr-xr-x   2 root    wheel      512 Dec 21  2012 rwho
drwxr-xr-x  11 root    wheel      512 Dec 31  2012 spool
drwxrwxrwt   3 root    wheel      512 Jan  9 03:30 tmp
drwxr-xr-x   2 root    wheel      512 Dec 21  2012 yp
You will notice that I deleted /Template/var/www but forgot to do that with /Template/var/mysql as well as to empty /Template/var/mail:
Code:
# ls -lh /Template/var/mail
total 6368
-rw-------  1 adriaan  adriaan   229K Dec 28  2014 adriaan
-rw-------  1 root     wheel     2.8M Jan 10 01:30 root
I am now going to do this on an Alix board with an recent OpenBSD version and will report my findings.
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Old 4 Weeks Ago
J65nko J65nko is offline
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Re: mfs size

You can use du(1) to find out the size in sectors for the -s option:
Code:
# du -s /var
115276  /var

# du -sh /var
56.3M   /var

# du -sh /Template/var
39.4M   /Template/var

# du -s /Template/var  
80752   /Template/var
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Old 4 Weeks Ago
J65nko J65nko is offline
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I just tested the procedure and it works on an Alix board with an OpenBSD current version of :
Code:
OpenBSD 5.8-current (GENERIC) #1430: Sat Dec 12 09:13:24 MST 2015
    deraadt@i386.openbsd.org:/usr/src/sys/arch/i386/compile/GENERIC
I have a attached a transcript (serial cable console connection) Please note that I use the more descriptive directory name /Template.mfs as source to populate the mfs.

An excerpt of the interesting part where the test directory /monkey is being edited into the /var.
Code:
    171 ------ So reboot works ....
    172 Now adjusting to really using /var instead of /monkey
    173 -------------------------------------------------------
    174 
    175 ------------ reboot to single user mode
    176 Note that I am connected with a serial console.
    177 Single user mode will stop networking, so if you are logged in with SSH you have a problem. ....
    178 
    179 --- see init(8) for more info about sending a 'TERM' signal to process nr 1 ...
    180 
    181 root@alix[~]kill -TERM 1
    182 Enter pathname of shell or RETURN for sh: 
    183 
    184 \u@\h[\w]                                                               
    185 \u@\h[\w]mount
    186 /dev/wd0a on / type ffs (local, noatime, softdep)
    187 /dev/wd0e on /home type ffs (local, noatime, nodev, nosuid, softdep)
    188 /dev/wd0d on /usr type ffs (local, noatime, nodev, softdep)
    189 
    190 -- So we lost our 'mfs' file system ...
    191 
    192 --- delete the contents of the /var directory, so we only have an empty
    193 --- /var directory as mount point for the mfs reincarnation of /var 
    194  
    195 \u@\h[\w]rm -r /var/*
    196 \u@\h[\w]ls -l /var
    197 
    198 \u@\h[\w]cat /etc/fstab
    199 72e6d0f437619269.b none swap sw
    200 72e6d0f437619269.a / ffs rw,noatime,softdep 1 1
    201 72e6d0f437619269.e /home ffs rw,noatime,softdep,nodev,nosuid 1 2
    202 72e6d0f437619269.d /usr ffs rw,noatime,softdep,nodev 1 2
    203 swap               /monkey mfs rw,noatime,nosuid,noexec,-P=/Template.mfs/var,-s=80000
    204 
    205 --- copy the /etc/fstab file
    206 
    207 \u@\h[\w]cp /etc/fstab /etc/fstab.orig
    208 
    209 --- test with sed(1) to change 'monkey' into 'var'
    210 
    211 \u@\h[\w]sed -e 's/monkey/var/' /etc/fstab.orig
    212 
    213 72e6d0f437619269.b none swap sw
    214 72e6d0f437619269.a / ffs rw,noatime,softdep 1 1
    215 72e6d0f437619269.e /home ffs rw,noatime,softdep,nodev,nosuid 1 2
    216 72e6d0f437619269.d /usr ffs rw,noatime,softdep,nodev 1 2
    217 swap               /var mfs rw,noatime,nosuid,noexec,-P=/Template.mfs/var,-s=80000
    218 
    219 --- Now the real thing ...
    220 
    221 \u@\h[\w]sed -e 's/monkey/var/' /etc/fstab.orig >/etc/fstab
    222 \u@\h[\w]cat /etc/fstab
    223 72e6d0f437619269.b none swap sw
    224 72e6d0f437619269.a / ffs rw,noatime,softdep 1 1
    225 72e6d0f437619269.e /home ffs rw,noatime,softdep,nodev,nosuid 1 2
    226 72e6d0f437619269.d /usr ffs rw,noatime,softdep,nodev 1 2
    227 swap               /var mfs rw,noatime,nosuid,noexec,-P=/Template.mfs/var,-s=80000
    228 
    229 --- Looks good so we can reboot 
    230 \u@\h[\w]reboot
    231 dd: /var/db/host.random: No such file or directory
    232 chmod: /var/db/host.random: No such file or directory
    233 dd: /var/db/host.random: No such file or directory
    234 single user: not running shutdown scripts
    235 syncing disks... done
    236 rebooting...
    252 root@alix[~]mount                                                       
    253 /dev/wd0a on / type ffs (local, noatime, softdep)
    254 /dev/wd0e on /home type ffs (local, noatime, nodev, nosuid, softdep)
    255 /dev/wd0d on /usr type ffs (local, noatime, nodev, softdep)
    256 mfs:1731 on /var type mfs (asynchronous, local, noatime, noexec, nosuid, size=80000 512-blocks)
    257 
    258 root@alix[~]ls -l /var
    259 total 40
    260 drwxr-xr-x  2 root  wheel      512 Dec 12 17:05 account
    261 drwxrws---  2 root  wheel      512 Dec 12 17:05 audit
    262 [snip]
    263 drwxr-xr-x  4 root  wheel      512 Dec 12 17:05 unbound
    264 drwxr-xr-x  2 root  wheel      512 Dec 12 17:06 yp
    265 
    266 root@alix[~]df -h
    267 Filesystem     Size    Used   Avail Capacity  Mounted on
    268 /dev/wd0a      873M   44.2M    785M     5%    /
    269 /dev/wd0e      376M    9.8M    348M     3%    /home
    270 /dev/wd0d      2.2G    185M    1.9G     9%    /usr
    271 mfs:1731      37.7M    3.5M   32.3M    10%    /var
    272 
    273 --- end of transcript (slightly edited of course ;) )
Re: /tmp directory

I don't think it worth to move /tmp to use a memory file system. It usually is empty.
Another reason is the following section of mount_mfs(1):
Code:
ENVIRONMENT
     TMPDIR  Directory in which to create temporary mount points for use by
             mount_mfs -P instead of /tmp.
I just wonder how that would work if /tmp is configured to be a memory file system....

Re: /dev

Some people also use a MFS for /dev. See https://www.mail-archive.com/openbsd.../msg01014.html

I will try that another day ...

BTW In case of questions you can use $ less -N alix-mfs.txt to see or refer to the line numbers of the transcript.
Attached Files
File Type: txt alix-mfs.txt (10.0 KB, 3 views)
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Quote:
Originally Posted by J65nko View Post
My defense: "Significant other" was already complaining why I still was at the computer, when we were supposed to be leaving for Eindhoven
Ahh, well then, case dismissed, we must all defer to a higher authority.
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mamalos mamalos is offline
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Thanks J65nko, you've been ridiculously helpful!

I haven't tested it yet, but I'll do it on Friday, so I'll come with news once it works.

If I encounter any problems after such an analytical explanation, I'll have to upgrade my IQ. Then I will ask for help.

Thanks again!!
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J65nko, I've tested it and it works fine. Thanks again!
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