path: root/doc/man/cgconfig.conf.5

.TH CGCONFIG.CONF 5
.\"***********************************
.SH NAME
cgconfig.conf \- libcgroup configuration file
.\"***********************************
.SH DESCRIPTION
.B "cgconfig.conf"
is the configuration file used by
.B libcgroup
to define control groups, their parameters and also mount points.
The file consists of
.I mount
and
.I group
sections.
These sections can be in arbitrary order.
Any line starting with '#' is considered as comment line and is
ignored.
.LP
.I mount
section has the form:
.RS
.nf
.ft B
.sp
mount {
.RS
.ft B
<controller> = <path>;
.I "..."
.RE
.ft B
}
.ft R
.fi
.RE

.TP
.B controller
Name of kernel subsystem. List of subsystems supported by kernel
can be found in 
.I /proc/cgroups
file.
.B Libcgroup
merges all subsystems mounted to the same directory (see
Example 1) and the directory is mounted only once.

.TP
.B 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.
.LP
.I group
section has the form:
.RS
.nf
.ft B
.sp
group <name> {
.RS
.ft B
[permissions]
<controller> {
.RS
.ft B
<param name> = <param value>;
.I "..."
.RE
.ft B
}
.I "..."
.RE
.ft B
}
.ft R
.fi
.RE

.TP
.B 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
.B 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.

.TP
.B permissions
Permissions of the given control group on mounted filesystem.
.I root
has always permission to do anything with the control group.
Permissions have the following syntax:
.RS 17
.ft B
.nf
perm {
.RS
.ft B
task {
.RS
.ft B
uid = <task user>;
gid = <task group>;
.RE
}
admin {
.RS
uid = <admin name>;
gid = <admin group>;
.RE
}
.RE
}
.fi
.RE
.ft R

.RS
.TP 17
.B "task user/group"
Name of the user and the group, which owns
.I tasks
file of the control group. I.e. this user and members of this
group has write access to the file.
.TP 17
.B "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.
.LP
Permissions are related only to enclosing control group and are not
inherited by subgroups. If there is no
.B perm
section in control group definition,
.I root:root
is owner of all files.
.RE
.TP
.B controller
Name of the kernel subsystem.
The section can be
empty, default kernel parameters will be used in this case. By
specifying
.B 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
.B 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.
.RS
.TP
.B param name
Name of the file to set. Each controller can have zero or more
parameters.
.TP
.B param value
Value, which should be written to the file when the control group is
created.
.RE

.\"********************************************"
.SH EXAMPLES
.LP
.SS Example 1
.LP
The configuration file:
.LP
.RS
.nf
mount {
.RS
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpu;
.RE
}
.fi
.RE

creates the hierarchy controlled by two subsystems, with no groups
inside. It corresponds to following operations:
.LP
.RS
.nf
mkdir /mnt/cgroups/cpu
mount -t cgroup -o cpu,cpuacct cpu /mnt/cgroups/cpu
.fi
.RE

.SS Example 2
.LP
The configuration file:
.LP
.RS
.nf
mount {
.RS
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpu;
.RE
}

group daemons/www {
.RS
perm {
.RS
task {
.RS
uid = root;
gid = webmaster;
.RE
}
admin {
.RS
uid = root;
gid = root;
.RE
}
.RE
}
cpu {
.RS
cpu.shares = 1000;
.RE
}
.RE
}

group daemons/ftp {
.RS
perm {
.RS
task {
.RS
uid = root;
gid = ftpmaster;
.RE
}
admin {
.RS
uid = root;
gid = root;
.RE
}
.RE
}
cpu {
.RS
cpu.shares = 500;
.RE
}
.RE
}
.RE
.fi
creates the hierarchy controlled by two subsystems with one group and
two subgroups inside, setting one parameter.
It corresponds to following operations:
.LP
.RS
.nf
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
.fi
.RE

The
.I 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.
.LP
Since both
.I cpuacct
and
.I cpu
subsystems are mounted to the same directory, all
groups are implicitly controlled also by
.I cpuacct
subsystem, even if there is no
.I cpuacct
section in any of the groups.
.RE

.SS Example 3
.LP
The configuration file:

.LP
.RS
.nf
mount {
.RS
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpuacct;
.RE
}

group daemons {
.RS
cpuacct{
}
cpu {
}
.RE
}
.fi
.RE
creates two hierarchies and one common group in both of them.
It corresponds to following operations:
.LP
.RS
.nf
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
.fi
.RE

In fact there are two groups created. One in
.I cpuacct
hierarchy, the second in
.I cpu
hierarchy. These two groups have nothing in common and can
contain different subgroups and different tasks.

.SS Example 4
.LP

The configuration file:

.LP
.RS
.nf
mount {
.RS
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpuacct;
.RE
}

group daemons {
.RS
cpuacct{
}
.RE
}

group daemons/www {
.RS
cpu {
.RS
cpu.shares = 1000;
.RE
}
.RE
}

group daemons/ftp {
.RS
cpu {
.RS
cpu.shares = 500;
.RE
}
.RE
}
.fi
.RE
creates two hierarchies with few groups inside. One of groups
is created in both hierarchies.

It corresponds to following operations:
.LP
.RS
.nf
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
.fi
.RE
Group
.I daemons
is created in both hierarchies. In
.I cpuacct
hierarchy the group is explicitly mentioned in the configuration
file. In 
.I cpu
hierarchy is the group created implicitly when
.I www
is created there. These two groups have nothing in common, for example
they do not share processes and subgroups. Groups
.I www
and
.I ftp
are created only in
.I cpu
hierarchy and are not controlled by
.I cpuacct
subsystem.

.SS Example 5
.LP
The configuration file:
.LP
.RS
.nf
mount {
.RS
cpu = /mnt/cgroups/cpu;
cpuacct = /mnt/cgroups/cpu;
.RE
}

group . {
.RS
perm {
.RS
task {
.RS
uid = root;
gid = operator;
.RE
}
admin {
.RS
uid = root;
gid = operator;
.RE
}
.RE
}
cpu {
}
.RE
}

group daemons {
.RS
perm {
.RS
task {
.RS
uid = root;
gid = daemonmaster;
.RE
}
admin {
.RS
uid = root;
gid = operator;
.RE
}
.RE
}
cpu {
}
.RE
}
.RE
.fi
creates the hierarchy controlled by two subsystems with one group with some
special permissions.
It corresponds to following operations:
.LP
.RS
.nf
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
.fi
.RE

Users, which are members of the 
.I 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
.I daemonmaster
group can move processes to
.I daemons
control group, but they can not move the process out of the group. Only
.I operator
or root can do that.

.SH RECOMMENDATIONS
.SS 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.

.SS Explicit is better than implicit
.B 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.

.SH FILES
.LP
.PD .1v
.TP 20
.B /etc/cgconfig.conf
.TP
default libcgroup configuration file
.PD 

.SH SEE ALSO
To be defined...

.SH BUGS
Parameter values can be only single string without spaces.
Parsing of quoted strings is not implemented.

.SH