Frequently Asked Questions
From Linux-VServer
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General
What is a 'Guest'?
What kind of Operating System (OS) can I run as guest?
Is this a new project? When was it started?
Which distributions did you test?
Is VServer comparable to XEN/UML/QEMU?
With which version should I begin?
Is VServer secure?
Performance?
What is the "great flower page"?
Resources usage
Resource sharing?
- memory: Dynamically.
- CPU usage: Dynamically (token bucket)
Resource limiting?
- using ulimits and rlimits (rlimit is a new feature of kernel 2.6/vs2.0.) per guest, to limit the memory consumption, the number of processes or file-handles, ... : see Resource Limits
- CPU usage : see CPU Scheduler
- disk space usage : see Disk Limits and Quota
How do I limit a guests RAM? I want to prevent OOM situations on the host!
If you want a recipe, do this:
- Check the size of memory pages. On x86 and x86_64 is usually 4 KB per page.
- Create /etc/vserver/<guest>/rlimits/
- Check your physical memory size on the host, e.g. with "free -m". maxram = kilobytes/pagesize.
- Limit the guests physical RAM to value smaller then maxram:
echo %%insertYourPagesHereSmallerThanMaxram%% > /etc/vserver/<guest>/rlimits/rss
- Check your swapspace, e.g. with 'swapon -s'. maxswap = swapkilobytes/pagesize.
- Limit the guest's maximum number of as pages to a value smaller than (maxram+maxswap):
echo %%desiredvalue%% > /etc/vserver/<guest>/rlimits/as
Disk I/O limiting? Is that possible?
# cat /sys/block/hdc/queue/scheduler noop [anticipatory] deadline cfq
The default is anticipatory a.k.a. "AS". When running several guests on a host you probably want the I/O performance shared in a fair way among the different guests. The kernel comes with a "completely fair queueing" scheduler, CFQ, which can do that. (More on schedulers can be found at http://lwn.net/Articles/114770/) This is how to set the scheduler to "cfq" manually:
root# echo "cfq" > /sys/block/hdc/queue/scheduler root# cat /sys/block/hdc/queue/scheduler noop anticipatory deadline [cfq]
Keep in mind that you have to do it on all physical discs. So if you run an md-softraid, do it to all physical /dev/hdXYZ discs! If you run Debian there is a predefined way to set the /sys values at boot-time:
# apt-get install sysfsutils [...] # grep cfq /etc/sysfs.conf block/sda/queue/scheduler = cfq block/sdc/queue/scheduler = cfq # /etc/init.d/sysfsutils restart
For non-vserver processes and CFQ you can set by which key the kernel decides about the fairness:
cat /sys/block/hdc/queue/iosched/key_type pgid [tgid] uid gid
Hint: The 'key_type'-feature has been removed in the mainline kernel recently. Don't look for it any longer :(
The default is tgid, which means to share fairly among process groups. Think every guest is treated like a own process group. It's not possible to set a scheduler strategy within a guest. All processes belonging to the same guest are treated like "noop" within the guest. So: If you run apache and some ftp-server within the _same_ guest, there is no fair scheduling between them, but there is fair scheduling between the whole guest and all other guests.
And: It's possible to tune the scheduler parameters in several ways. Have a look at /sys/block/hdc/queue/....
Nice disk I/O scheduling, is that possible?
It's split into three groups, called real-time, best effort and idle. The default is best-effort, but within best-effort, you can have a niceness from 0 to and including 7. You can set this niceness by the tool ionice, which for debian is either in the package util-linux or schedutils. To change the io-niceness you need the CAP_SYS_NICE, and need to have the same uid as the processe you want to ionice.
- Note: If you want to use any schedulung other than best-effort you will also need the CAP_SYS_ADMIN-flag. Be warned that this gives quite some capabilities to the vserver, not just for I/O scheduling!
If you want to increase the niceness of an I/O hogging process within a vserver you need to do:
chcontext --xid sponlp1 sudo -u '#2089' ionice -c2 -n5 -p24409with sudo and ionice installed on the root server to increase the *nice*ness of pid 24409, with uid 2089
Unification
What is unification (vunify)?
What is vhashify?
It creates hardlinks to files named after a hash of the content of the file. If you have a recent version of the vserver patch (2.2+), with CONFIG_VSERVER_COWBL enabled, you can even modify the hardlinked files inside the vservers and the links will be broken automatically.
There seems to be a catch when a hashified file has multiple hardlinks inside a guest, or when another internal hardlink is added after hashification. Link breaking will remove all the internal hardlinks too, so the guest will end up with different copies of the original file. The correct solution would be to not hashify files that have multiple links prior to hashification, and to break the link to the hashified version when a new internal hardlink is created. Apparently, this is not implemented yet (?).
How do I manage a multi-guest setup with vhashify?
mkdir /etc/vservers/.defaults/apps/vunify/hash /vservers/.hash ln -s /vservers/.hash /etc/vservers/.defaults/apps/vunify/hash/root
Then, do this one line per vserver:
mkdir /etc/vservers/<vservername>/apps/vunify # vhashify reuses vunify configuration
To hashify a running vserver, do (possibly from a cronjob):
vserver name-of-guest hashify
The guest needs to be running because vhashify tries to figure out what files not to hashify by calling the package manager of the guest via vserver enter.
In order for the OS cache to benefit from the hardlinking, you'll have to restart the vservers.
To clean up hashified files that are no longer referenced by any vserver, do (possibly from a cronjob):
find /vservers/.hash -type f -links 1 -print0 | xargs -0 rmUntil you do this, the files still take up place even though no vservers need them.
Filesystem usage
Is there a way to implement "user/group quota" per VServer?
What about "Quota" for a context? Howto limit disk usage?
How do I tag a guest's directory with xid?
Filesystem XID tagging only works on supported filesystem. Those are currently: ext2/3, reiserfs/reiser3, xfs and jfs. To activate the XID tagging you have to mount the filesystem with "-o tag" (former tagxid is outdated since VS2.2). Attention: It's _not_ possible to "-o remount,tag", you have to mount it freshly. The guests will tag their files automatiaclly. If you copy files in from the host, you have to tag them manually like this:
chxid -c xid -R /var/lib/vservers/<guest>
Note: Context 0 and 1 will see all files, guests will only be able to access untagged files and their own XID. They can see other XID files but no information about the file, e.g. no owner, no group, no permissions.
Note: It is not advised to tag the root filesystem, as explained by Herbert : trying to do so will expose you to some troubles !
Network
Does it support IPv6?
I can't do all I want with the network interfaces inside the guest?
How do I add several IPs to a vserver?
Here is a little helper-script that adds a list of IPs defined in a text file, one per line.
#!/bin/bash j=1 for i in `cat myiplist`; do j=$(($j+1)) mkdir $j echo $i > $j/ip echo "24" > $j/prefix done
How do I assign a new IP address to a running guest?
- add the ip on the host, for example
ip addr add 194.169.123.23/24 dev eth0
- add the ip to the guest's network context (a guests NID is the same as the XID {context ID})
naddress --add --nid <nid> --ip 194.169.123.23/24
- enter the guest (best via ssh)
- restart the services that need to make use of the new address if required
- update the config in /etc/vserver/<servername>/interfaces to reflect the changes for the next guest restart (if desired)
If my host has only one a single public IP, can I use RFC1918 IP (e.g. 192.168.foo.bar) for the guest vservers?
iptables -t nat -I POSTROUTING -s $VSERVER_NETZ ! -d $VSERVER_NETZ -j SNAT --to $EXT_IP
See: HowtoPrivateNetworking and
http://www.tgunkel.de/it/software/doc/linux_server.en#h3-VServer_Masquerading_SNAT (THX, [MUPPETS]Gonzo)
If I shut down my vserver guest, the whole Internet interface ethX on the host is shut down. What happened?
Can I run an OpenVPN Server in a guest?
This is the minimal OpenVPN configuration for the Server which will be used to demonstrate how to get it running in a client:
# Networking setup server 192.168.16.0 255.255.255.0 dev tun16 ifconfig-noexec comp-lzo # Certificates dh ... ca ... cert ... key ... # Management persist-key keepalive 10 60 verb 4
First of all you have to prepare the host with a persistent interface in the right mode and with the right settings. This is easily done by using openvpn and the ip and route tools.
# openvpn --mktun --dev tun16 # ip link set dev tun16 txqueuelen 100 # ifconfig tun16 192.168.16.1 pointopoint 192.168.16.2 mtu 1500 # route add -net 192.168.16.0 netmask 255.255.255.0 gw 192.168.16.2
If you need different settings, openvpn will tell you the ifconfig and route commands it uses to configure the interface when being started on the host with the original config file, but without ifconfig-noexec. Additionally, the guest needs /dev/net/tun to make OpenVPN happy. This can be created with MAKEDEV:
# cd /var/lib/vserver/<myopenvpnserver>/dev/ # ./MAKEDEV tun (creates the dev/net/tun device accessible by the guest - even a tap interface needs /dev/net/tun !)
Finally, the guest needs to have the tun device assigned:
# head /etc/vservers/<myopenvpnserver>/interfaces/1/* ==> /etc/vservers/<myopenvpnserver>/interfaces/1/ip <== 192.168.16.1 ==> /etc/vservers/<myopenvpnserver>/interfaces/1/nodev <== tun16 ==> /etc/vservers/<myopenvpnserver>/interfaces/1/prefix <== 24 #
The client's conf may look like that:
# Basic setup client proto tcp-client dev tun remote <ipaddress> comp-lzo verb 4 # Certificate ca ...[ Based on derJohn's original answer, all errors mine ]
Trying to connect to a vserver from the host or another vserver on the same host fails
sin_addr=inet_addr("xx.xx.xx.xx")}, yy) = -1 EINVAL (Invalid argument)
A: The host/guest cannot communicate with another guest on same host.
- check all netmasks on all interfaces (do they overlap) ?
- check policy routing (disable it temporary) ?
- check that lo is up (Networking within a host/guest always uses lo interface)
Can I use iptables ?
Administration tools
Which guest vservers are running?
CTX PROC VSZ RSS userTIME sysTIME UPTIME NAME 0 77 965.1M 334.6M 14m14s18 2m28s69 1h33m46 root server 49152 7 14M 5.2M 0m00s40 0m00s30 1h30m15 chiffon
Is there a web-based interface for vserver that will allow creation/deletion/configuration etc. of vserver guests?
- http://Openvcp.org which is a distributed system (agent!) with a web-interface, with which you can build/remove guests
- http://vsmon.revolutionlinux.com/ is a distributed monitoring-only solution that allows you to search for a particular vserver in your park.
Hosting foreign distributions
I run a Debian host and want to build an Ubuntu guest. Howto?
vserver vubuntu build --force -m debootstrap --hostname vubuntu.myvservers.net --netdev eth0 --interface 192.168.0.2/24 \ --context 42 -- -d breezy -m http://de.archive.ubuntu.com/ubuntu
[UPDATE] Currently there are problems in building breezy under unclear circumstances, which seems to have to do with udev. If the above didnt work, try:
vserver vubuntu build --force -m debootstrap --hostname vubuntu.myvservers.net --netdev eth0 --interface 192.168.0.2/24 \ --context 42 -- -d breezy -m http://de.archive.ubuntu.com/ubuntu -- --exclude=udev
In very recent versions of the utils, the problem should not occur anymore (it has to do with the 'secure-mount' if you look in the MLs)
Well, sid's debootstrap knows how to bootstrap Ubuntu linux. Make sure to have a current debootstrap package:
apt-get update apt-get install debootstrapThe knowledge how to build ubuntu 'breezy badger' (which you probably want to be your guest at the time of writing) has been added recently.
I want to build a Gentoo guest. Howto?
Application level problems
I did everything right, but the application foo does not start. What's up there?
When I try to ssh to the guest, I log into the host, even if I installed sshd on the guest. What's wrong here?
Port 22 # Use these options to restrict which interfaces/protocols sshd will bind to #ListenAddress ::
And now change the setting to
Port 22 # Use these options to restrict which interfaces/protocols sshd will bind to ListenAddress your.hosts.ip.here # not the guests IP!
Then '/etc/init.d/ssh restart' on the host, after that on the guest (if you did apt-get install ssh on the guest already.) Do I have to explain more? If the hosts sshd binds all available IP addresses on port 22 (The hosts 'sees' even all addresses of the guests!). So if the guest starts its sshd, it can't bind to port 22 any more. You need to change that setting only on the host.
(BTW: A similar approach has to be done for a lot of daemons, e.g. Apache. If the daemon does not support an explicit bind, you may use the chbind command to 'hide' IP addresses from the daemon before starting.)
Bind9 does not like to start in my guest.
My mysqld running in a guest behaves strangely and is awfully slow/locks up
Pure-FTP does not run inside a VServer?
Why do neither sshd nor crond (vixie-cron) work correctly in my CentOS / Fedora guest? I get 'pam_loginuid(crond:session): set_loginuid failed opening loginuid' and similar lines in my logs.
pam authentication (also used with openssh) enables "pam_loginuid.so" in the /etc/pam.d/* files. Comment those out as they are not necessary and will not load within a guest anyway. This probably is also necessary on updates later on, if the configs get changed. You therefore may add the following command line to a cronjob file or your software update script:
/bin/sed --in-place -e "s/^session.*required.*pam_loginuid.so/# session\trequired\tpam_loginuid.so/g" /etc/pam.d/*
How do i install nagios-plugins on a Gentoo guest?
The easiest way to do this from the host (assuming the guest is running) is:
vnamespace -e <xid> -- chroot /vservers/<name> emerge nagios-plugins -va
Somebody runs ntpd in guest and you can't use ntpdate in host?
ntpdate -u ntp.domain.xy
or you can use command:
chbind --nid 42 --ip 1.2.3.4 -- ntpdate ntp.domain.xywhere IP will be the IP of host.
Start / Stop a VServer
How do I make a vserver guest start by default?
echo "default" > /etc/vservers/derjohn/apps/init/mark
If you want to start it earlier, please read the init script "/etc/init.d/util-vserver" to find out how to do it. In most cases you don't need to change this. On Debian the vservers are started at "20", so after most other stuff is up (networking etc.).
Besides that I created a small helper script for managing the autostart foo: ((vserver-autostart))
My host works, but when I start a guest it says that it has a problem with chbind.
What is old-style and new-style config?
How can I reboot/halt guests?
For legacy Linux-VServer (i.e. 1.2.x), you have to replace /sbin/halt in the guests with vreboot and start rebootmgr in the host. You also need to have a <guest>.conf file in /etc/vservers for each guest. Please have a look at /etc/init.d/rebootmgr.
For Linux-VServer 2.0+, sys_reboot has been virtualized to do the right thing. No changes are needed in guests.
What is the initial PATH?
When I try to start a guest i get this message "/proc/uptime can not be accessed. Usually, this is caused by procfs-security. Please read the FAQ for more details"?
Kernel
Is SMP Supported?
Do I really need the legacy-interfaces? What are these legacy-interfaces?
I have a vserver running on a Linux kernel with preemption. Is VServer "preempt" safe?
32 vs 64 Bit? What should I take?
[*] Kernel support for ELF binaries <M> Kernel support for MISC binaries [*] IA32 Emulation <---- without that, the entire 32bit API is not present <M> IA32 a.out support
You can force the guest to behave like a 32 environment like this:
echo linux_32bit > /etc/vservers/$NAME/personality echo i686 > /etc/vservers/$NAME/uts/machine
(thanks cehteh for the hint!)
But you can force debootstrap to put 32 bit binaries into the guest by 'export ARCH=i386';
export ARCH=i386 ; vserver build ....
Distribution specific questions
VServer is included in the stable Debian GNU/Linux for years now. What VS version did they include?
Were can I get newer versions of VServer as ready made packages for Debian?
Misc
Why isn't there a device /dev/xyz within a guest?
I want to (re)mount a partition in a running guest ... but the guest has no rights (capability) to (re)mount?
# vnamespace -e XID mount -t tmpfs -o remount,size=256m,mode=1777 none /var/lib/vservers/<guest>/tmp/
(if there's a problem, try expanding the symlinks in the mount path)
Be warned that the guest will not recognize the change, as the /etc/mtab file is not updated when you mount like this. To permanently change the mount, edit /etc/vserver/<guest>/fstab on the host.
Does anyone know how to increase the size of /tmp within a vserver w/o restarting?
# vnamespace -e XID mount -n -t tmpfs -o remount,size=32m tmpfs /<vdir>/<guest>/tmp
or something like that. The arguments are needed since mount is not going to be using /etc/fstab for the information and the version of /proc/mounts is best understood by
# vnamespace -e XID cat /proc/mounts.See Frequently_Asked_Questions#I want to (re)mount a partition in a running guest ... but the guest has no rights (capability) to (re)mount?
#1 ERROR: capset(): Operation not permitted
How can I make 'vserver start' mount the root filesystem?
/dev/drbd0 / xfs rw,dev 0 0
I deleted a guest's directory without shutting it down. Now I have a "ghost" running. Is there any possibility to get it out of proc without rebooting?
When using nice and su (for example, in the updatedb cron job), I get: su: Permission denied. What does it mean?
$ strace nice su nobody [...] setpriority(PRIO_PROCESS, 0, 0) = -1 EACCES (Permission denied)
You can use 'su nobody -c nice some_cmd' instead.
(Now there's the question of why a guest process cannot lower its nice value.)
How do I handle NFS mounts within in a guest?
1) Mount the NFS share from the host OS and let vserver guest access it as part of it's file system.
mount --bind may also be beneficial in this scenario.
2) Use util-vserver and create a fstab.remote file in the /etc/vserver/<vserver_name> directory. Populate this with the NFS shares and they will be mounted in the context of the vserver guest.
See http://www.nongnu.org/util-vserver/doc/conf/configuration.html
3) Add capabilities to the vserver guest instance to grant sufficient rights to allow NFS mounts.
Add the following to /etc/vserver/<vserver_name>/bcapabilities
SYS_ADMIN
Add the following to /etc/vserver/<vserver_name>/ccapabilities
SECURE_MOUNT BINARY_MOUNT
See Capabilities_and_Flags for more information about vserver capabilities.
If you want the NFS shares to be mounted when the guest starts, add them to /etc/vserver/<vserver_name>/fstab
vserver start/stop/enter fails with something like "vnamespace: execvp("/usr/sbin/vserver"): No such file or directory" ?
vnamespace -e <guest> cat /proc/mounts
If there is no /usr, you can fix your problem with simply mounting it using the following command:
vnamespace -e <guest> mount /dev/<device> /usr
Upgrade from 2.0 to 2.2
I now get errors like "ncontext: vc_net_create(): Invalid argument; dynamic contexts disabled." on startup. Vservers are not started
echo 101 > /etc/vservers/myvserv/contextADDENDUM: please consider that valid static contexts are between 2 and 49151 ( daniel_hozac on IRC ) otherwise you will end up with unexplainable error "ncontext: vc_net_migrate(): No such process" when trying to start the vserver.
How do I assign a static context to an existing vserver?
Since upgrading to a newer VS version my guest complains about "vsched: non-numeric value specified for '--priority_bias" at start time. What's wrong?
# cat /usr/local/sbin/vserver-convert-schedule-to-scheddir #/bin/sh mkdir /etc/vservers/$1/sched sed -e 1p -n /etc/vservers/$1/schedule > /etc/vservers/$1/sched/fill-rate sed -e 2p -n /etc/vservers/$1/schedule > /etc/vservers/$1/sched/interval sed -e 3p -n /etc/vservers/$1/schedule > /etc/vservers/$1/sched/tokens sed -e 4p -n /etc/vservers/$1/schedule > /etc/vservers/$1/sched/tokens-min sed -e 5p -n /etc/vservers/$1/schedule > /etc/vservers/$1/sched/tokens-max mv /etc/vservers/$1/schedule /etc/vservers/$1/schedule.converted.see.scheddir # see: http://oldwiki.linux-vserver.org/Scheduler+Parameters # see: http://www.nongnu.org/util-vserver/doc/conf/configuration.html#sched
Here is an example how to do so:
# mkdir /etc/vservers/<vserver>/sysctl/0 -p # echo kernel.shmall > /etc/vservers/<vserver>/sysctl/0/setting # echo 134217728 > /etc/vservers/<vserver>/sysctl/0/value # mkdir /etc/vservers/<vserver>/sysctl/1 -p # echo kernel.shmmax > /etc/vservers/<vserver>/sysctl/1/setting # echo 134217728 > /etc/vservers/<vserver>/sysctl/1/value
It's also explained on the geat flower page:
- see: http://www.nongnu.org/util-vserver/doc/conf/configuration.html -> Look for "sysctl".
After changing those values, restart your guest, enter it and check if the values are set:
# sysctl -a | grep shm ... kernel.shmall = 134217728 kernel.shmmax = 134217728