NAME
cgconfig.conf - libcgroup configuration file
DESCRIPTION
cgconfig.conf is the configuration file used by libcgroup to define
control groups, their parameters and also mount points. The file
consists of mount and group sections. These sections can be in
arbitrary order. Any line starting with '#' is considered as comment
line and is ignored.
mount section has the form:
mount {
<controller> = <path>;
...
}
controller
Name of kernel subsystem. List of subsystems supported by kernel
can be found in /proc/cgroups file. Libcgroup merges all
subsystems mounted to the same directory (see Example 1) and the
directory is mounted only once.
path The directory path, where group hierarchy associated to given
controller, shall be mounted. The directory is created
automatically on cgconfig service startup if it does not exist
and is deleted on service shutdown.
group section has the form:
group <name> {
[permissions]
<controller> {
<param name> = <param value>;
...
}
...
}
name Name of the control group. It can contain only characters, which
are allowed for directory names. The groups form a tree, i.e. a
control group can contain zero or more subgroups. Subgroups can
be specified using '/' delimiter.
The root control group is always created automatically in all
hierarchies and it is the base of the group hierarchy. It can be
explicitly specified in cgconfig.conf file by using '.' as group
name. This can be used e.g. to set its permissions, as shown in
Example 5.
When the parent control group of a subgroup is not specified,
then it is created automatically.
permissions
Permissions of the given control group on mounted filesystem.
root has always permission to do anything with the control
group. Permissions have the following syntax:
perm {
task {
uid = <task user>;
gid = <task group>;
}
admin {
uid = <admin name>;
gid = <admin group>;
}
}
task user/group Name of the user and the group, which owns
tasks file of the control group. I.e. this user
and members of this group has write access to
the file.
admin user/group Name of the user and the group, which owns the
rest of control group's files. These users are
allowed to set subsystem parameters and create
subgroups.
Permissions are related only to enclosing control group and are
not inherited by subgroups. If there is no perm section in
control group definition, root:root is owner of all files.
controller
Name of the kernel subsystem. The section can be empty, default
kernel parameters will be used in this case. By specifying
controller the control group and all its parents are controlled
by the specific subsystem. One control group can be controlled
by multiple subsystems, even if the subsystems are mounted to
different directories. Each control group must be controlled by
at least one subsystem, so libcgroup knows, in which hierarchies
the control group should be created.
The parameters of given controller can be modified in following
section enclosed in brackets.
param name
Name of the file to set. Each controller can have zero or
more parameters.
param value
Value, which should be written to the file when the
control group is created.
EXAMPLES
Example 1
The configuration file:
mount {
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpu;
}
creates the hierarchy controlled by two subsystems, with no groups
inside. It corresponds to following operations:
mkdir /mnt/cgroups/cpu
mount -t cgroup -o cpu,cpuacct cpu /mnt/cgroups/cpu
Example 2
The configuration file:
mount {
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpu;
}
group daemons/www {
perm {
task {
uid = root;
gid = webmaster;
}
admin {
uid = root;
gid = root;
}
}
cpu {
cpu.shares = 1000;
}
}
group daemons/ftp {
perm {
task {
uid = root;
gid = ftpmaster;
}
admin {
uid = root;
gid = root;
}
}
cpu {
cpu.shares = 500;
}
}
creates the hierarchy controlled by two subsystems with one group and
two subgroups inside, setting one parameter. It corresponds to
following operations:
mkdir /mnt/cgroups/cpu
mount -t cgroup -o cpu,cpuacct cpu /mnt/cgroups/cpu
mkdir /mnt/cgroups/cpu/daemons
mkdir /mnt/cgroups/cpu/daemons/www
chown root:root /mnt/cgroups/cpu/daemons/www/*
chown root:webmaster /mnt/cgroups/cpu/daemons/www/tasks
echo 1000 > /mnt/cgroups/cpu/daemons/www/cpu.shares
mkdir /mnt/cgroups/cpu/daemons/ftp
chown root:root /mnt/cgroups/cpu/daemons/ftp/*
chown root:ftpmaster /mnt/cgroups/cpu/daemons/ftp/tasks
echo 500 > /mnt/cgroups/cpu/daemons/ftp/cpu.shares
The daemons group is created automatically when its first subgroup is
created. All its parameters have the default value and only root can
access group's files.
Since both cpuacct and cpu subsystems are mounted to the same
directory, all groups are implicitly controlled also by cpuacct
subsystem, even if there is no cpuacct section in any of the groups.
Example 3
The configuration file:
mount {
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpuacct;
}
group daemons {
cpuacct{
}
cpu {
}
}
creates two hierarchies and one common group in both of them. It
corresponds to following operations:
mkdir /mnt/cgroups/cpu
mkdir /mnt/cgroups/cpuacct
mount -t cgroup -o cpu cpu /mnt/cgroups/cpu
mount -t cgroup -o cpuacct cpuacct /mnt/cgroups/cpuacct
mkdir /mnt/cgroups/cpu/daemons
mkdir /mnt/cgroups/cpuacct/daemons
In fact there are two groups created. One in cpuacct hierarchy, the
second in cpu hierarchy. These two groups have nothing in common and
can contain different subgroups and different tasks.
Example 4
The configuration file:
mount {
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpuacct;
}
group daemons {
cpuacct{
}
}
group daemons/www {
cpu {
cpu.shares = 1000;
}
}
group daemons/ftp {
cpu {
cpu.shares = 500;
}
}
creates two hierarchies with few groups inside. One of groups is
created in both hierarchies.
It corresponds to following operations:
mkdir /mnt/cgroups/cpu
mkdir /mnt/cgroups/cpuacct
mount -t cgroup -o cpu cpu /mnt/cgroups/cpu
mount -t cgroup -o cpuacct cpuacct /mnt/cgroups/cpuacct
mkdir /mnt/cgroups/cpuacct/daemons
mkdir /mnt/cgroups/cpu/daemons
mkdir /mnt/cgroups/cpu/daemons/www
mkdir /mnt/cgroups/cpu/daemons/ftp
Group daemons is created in both hierarchies. In cpuacct hierarchy the
group is explicitly mentioned in the configuration file. In cpu
hierarchy is the group created implicitly when www is created there.
These two groups have nothing in common, for example they do not share
processes and subgroups. Groups www and ftp are created only in cpu
hierarchy and are not controlled by cpuacct subsystem.
Example 5
The configuration file:
mount {
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpu;
}
group . {
perm {
task {
uid = root;
gid = operator;
}
admin {
uid = root;
gid = operator;
}
}
cpu {
}
}
group daemons {
perm {
task {
uid = root;
gid = daemonmaster;
}
admin {
uid = root;
gid = operator;
}
}
cpu {
}
}
creates the hierarchy controlled by two subsystems with one group with
some special permissions. It corresponds to following operations:
mkdir /mnt/cgroups/cpu
mount -t cgroup -o cpu,cpuacct cpu /mnt/cgroups/cpu
chown root:operator /mnt/cgroups/cpu/*
chown root:operator /mnt/cgroups/cpu/tasks
mkdir /mnt/cgroups/cpu/daemons
chown root:operator /mnt/cgroups/cpu/daemons/*
chown root:daemonmaster /mnt/cgroups/cpu/daemons/tasks
Users, which are members of the operator group are allowed to
administer the control groups, i.e. create new control groups and can
move processes between these groups without having root privileges.
Members of daemonmaster group can move processes to daemons control
group, but they can not move the process out of the group. Only
operator or root can do that.
RECOMMENDATIONS
Keep hierarchies separated
Having multiple hierarchies is perfectly valid and can be useful in
various scenarios. To keeps things clean, do not create one group in
multiple hierarchies. Examples 3 and 4 shows, how unreadable and
confusing it can be, especially when reading somebody others
configuration file.
Explicit is better than implicit
libcgroup can implicitly create groups which are needed for creation of
configured subgroups. This may be useful and save some typing in simple
scenarios. When it comes to multiple hierarchies, it's better to
explicitly specify all groups and all controllers related to them.
FILES
/etc/cgconfig.conf
default libcgroup configuration file
SEE ALSO
To be defined...
BUGS
Parameter values can be only single string without spaces. Parsing of
quoted strings is not implemented.