Solved How can I identify the OS installed in each jail?

[Jim L.]

I'd like to be able to configure my jails with some local variables that don't need to be passed to the kernel during jail(8) creation. I can set one, and jail -e \; will display it:

 ...;X.my_variable=my_value;...

but it causes an error when starting the jail:

jail: my_jail: unknown parameter: X.my_variable

I was hoping there might be some reserved namespace for user-defined config variables that I could use in lieu of X

While I believe this would be generally useful, especially if perhaps these user-defined variables got inherited by the jail's environment, my specific objective is to be able to identify what OS is installed in each jail. There is a variable security.jail.param.linux.osname, but it doesn't seem to accept an arbitrary string value when defined in jail.conf.

# sysctl -d security.jail.param.linux.osname security.jail.param.host.hostname security.jail.param.host.domainname
security.jail.param.linux.osname: Jail Linux kernel OS name
security.jail.param.host.hostname: Jail hostname
security.jail.param.host.domainname: Jail NIS domainname

My current jail.conf does not set any of those, yet they have somewhat puzzling default values:

# for j in 7 8 9 10; do sysctl -j $j security.jail.param.linux.osname security.jail.param.host.hostname \
           security.jail.param.host.domainname; echo --; done
security.jail.param.linux.osname: 65
security.jail.param.host.hostname: 256
security.jail.param.host.domainname: 256
--
security.jail.param.linux.osname: 65
security.jail.param.host.hostname: 256
security.jail.param.host.domainname: 256
--
security.jail.param.linux.osname: 65
security.jail.param.host.hostname: 256
security.jail.param.host.domainname: 256
--
security.jail.param.linux.osname: 65
security.jail.param.host.hostname: 256
security.jail.param.host.domainname: 256

The actual OSes in those jails are:

# for j in 7 8 9 10; do jexec $j uname -a; done
FreeBSD webwork2.example.edu 14.3-BETA2 FreeBSD 14.3-BETA2 releng/14.3-n271377-0e8065166204 GENERIC amd64
FreeBSD listserv.example.edu 14.3-BETA2 FreeBSD 14.3-BETA2 releng/14.3-n271377-0e8065166204 GENERIC amd64
FreeBSD aarch64.example.edu 14.3-BETA2 FreeBSD 14.3-BETA2 releng/14.3-n271377-0e8065166204 GENERIC amd64
Linux ubuntu 5.15.0 FreeBSD 14.3-BETA2 releng/14.3-n271377-0e8065166204 GENERIC x86_64 x86_64 x86_64 GNU/Linux
# jexec 10 lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 24.04.2 LTS
Release:        24.04
Codename:       noble

But when I set the config to be:

name=ubuntu-23;path=/jail/ubuntu-23.10;interface=private;mount.devfs;exec.clean;exec.jail_user=root;exec.start="/etc/init.d/rc 3";
exec.stop="/etc/init.d/rc 0";exec.consolelog=/var/log/jail_ubuntu-23.log;exec.system_user=root;allow.raw_sockets;allow.mount=1;
allow.set_hostname=0;allow.sysvipc=0;security.jail.param.linux.osname="Ubuntu 24.04.2 LTS";host.hostname=ubuntu;persist;
sysvmsg=inherit;sysvsem=inherit;sysvshm=inherit;enforce_statfs=1;devfs_ruleset=7;ip4.addr=192.168.1.8;mount.fstab=/etc/fstab.ubuntu23

the jail again refuses to start and complains unknown parameter: security.jail.param.linux.osname

What can I do to query the OS inside a jail other than jexec trickery? A jexec-based query of course requires the jail to be running, whereas I'd prefer to be able to query even stopped jails, based on their jail.conf settings.

 

[Jim L.]

Figured it out .... I should have been paying more attention to jail(8) instead of sysctl(8).

Early on in /etc/jail.conf, up high in the global defaults:

# Jail defaults:
... the usual defaults ...
linux.osname        = 'FreeBSD';    # default OS name

In /etc/jail.conf.d/ubuntu-23.conf:

linux.osname    = "Ubuntu 24.04.2 LTS";

Then I can display the raw config file data:

# jail -e \; | egrep -o '(^|;)(path|linux\.osname)=[^;]+' | sed -e 's/^;//'
linux.osname=FreeBSD
path=/jail/aarch64
linux.osname=FreeBSD
path=/jail/mailman
linux.osname=FreeBSD
path=/jail/mailman2
linux.osname="Ubuntu 24.04.2 LTS"
path=/jail/ubuntu-23.10
linux.osname=FreeBSD
path=/jail/webwork2

Or I can use jls to query the OS type of just the currently running jails:

# service jail restart
....
# jls -s jid host.hostname path linux.osname
jid=20 host.hostname=webwork2.example.edu path=/jail/webwork2 linux.osname=FreeBSD
jid=21 host.hostname=listhost.example.edu path=/jail/mailman2 linux.osname=FreeBSD
jid=22 host.hostname=aarch64.example.edu path=/jail/aarch64 linux.osname=FreeBSD
jid=23 host.hostname=ubuntu path=/jail/ubuntu-23.10 linux.osname="Ubuntu 24.04.2 LTS"