plan9front/sys/man/8/gefs

.TH GEFS 8
.SH NAME
gefs \- file server maintenance
.SH SYNOPSIS
.PD 0
.PP
.B check
.PP
.B df
.PP
.B halt
.PP
.B help
.PP
.B permit
[
.B on
|
.BR off
]
.PP
.B save trace
.I filename
.PP
.B snap
[
-Smdl
]
[
.I old 
[
.I new
]
]
.PP
.B sync
.PP
.B users
.SH DESCRIPTION
.IR Gefs (4)
provides an administration console on
.IR /srv/gefs.cmd .
By default, this console is only readable
and writable by the owner of the file system.
.SH CONSOLE
.PP
The console handles the following commands:
.PP
.I Check
applies basic consistency checks to the file system,
reporting invalid blocks, broken metadata, and other
similar structural issues.
.PP
.I Df
prints the amount of used space and total space in megabytes,
as well as the percentage of space occupied.
.PP
.I Halt
syncs all IO to disk and exits the file system.
While the syncing occurs, the file system does not
allow new writes.
.PP
.I Help
prints a summary of the available commands.
This table includes additional debug commands that are
subject to change, and are intentionally undocumented.
.PP
.I Permit
[
.B on
|
.B off
]
has two effects.
First, if the user table is broken, it allows a fallback to a default user list.
This allows the system administrator to recover if they reboot with a broken user file.
Second, it allows mounts to occur in permissive mode by any user.
Permissive mounts are designated by prefixing the attach spec with a
.I %
sigil.
Permissive disables permissions checks when accessing files, and allows
.IR wstat (5)
to modify the owner of the file.
This may be useful during file system initialization.
.PP
.B Snap
manages snapshots.
It can be invoked as
.I snap
.BR -l ,
.I snap
.B -d
.IR snap ,
or
.I snap
[
.B -flags
]
.IR "old new" ,
which will list, delete, or create new snapshots respectively.
It accepts the following options:
.TP
.B -l
Lists snapshots and their attributes.
.TP
.BI "-d " snap
Deletes a snapshot, reclaiming whatever space is not shared
is not shared with other snapshots.
.TP
.B -m
Flags that the newly created snapshot should be mutable.
.TP
.B -S
Disables automatic snapshots.
.I old
and gives it the name
.IR new .
.PP
.I Sync
writes dirty blocks in memory to the disk.
.PP
.B Users
attempts to reload the user table from
.IR /adm/users .
.PP
.I Save trace
saves a trace of recent operations to a file.
If a file is not specified, it prints to the console.
.SH SNAPSHOTS
Snapshots are independent views of a filesystem hierarchy.
A snapshot may be mutable or immutable.
Mutable snapshots can be mounted and written to,
Immutable snapshots are a view of a file system hierarchy at a point im time.
They are referred to by name, and are selected at mount time with an attach spec.
When the attach spec starts with the
.B %
sigil, a snapshot is mounted in permissive mode.
This allows the mounting user to bypass normal file system permission checks.'
In order to mount a snapshot in permissive mode, the mounting user must be in the
.I adm
group.
.PP
There are several attach names that are reserved for the file system's internal use.
All of these other than the
.I main
snapshot are required for the file system to work correctly, and may not be removed.
.TP
.I dump:
This is the name used to mount a list of all snapshots.
Each snapshot in the file system will be listed in a directory.
.TP
.I empty:
This is a read-only empty snapshot.
It contains no files or directories.
The empty snapshot may be forked in order to create a new hierarchy,
independent of other snapshots.
.TP
.I adm:
This is the snapshot where administrative files live.
The
.I users
file is read at gefs startup, and define the users and groups for all snapshots.
This file is described in detail in the following section.
.TP
.I main:
This snapshot is less special than the other special snapshots.
It is created by default at file system mount time,
and is the snapshot which is mounted when an attach specifier is not given.
However, it is otherwise not special.
It may be deleted, created, and freely modified.
.PP
All snapshots are allocated from the same storage pool, and therefore
share space.
.SH ADM FILES
.PP
Gefs supports independent snapshots in the same file system.
As a result, global configuration needs to be separated from snapshots.
The global configuration resides in a well known snapshot called
.IR adm .
.PP
The adm snapshot would conventionally be mounted in
.IR /adm .
It contains the
.IR users (6)
file.
.IR
The
.I users
file is read at file system startup, or when the
.I users
command is run on the console.
If the users file is malformed at file system start, then the file system will refuse to initialize.
.I Permissive
mode will allow the file system to fall back to a default users table.
It will also allow any user to mount the
.I adm
snapshot: this can help recover from disasters.
.PP
The
.B default
table looks like this:
.IP
.EX
-1:adm:adm:
0:none::
1:$user:$user:
.EE
.PP
Where
.I $user
is specified at the time that the file system is reamed.
.SH EXAMPLES
.PP
To show current disk usage, the following may be written on the console:
.IP
.EX
gefs# df
.EE
.PP
To create a new snapshot:
.IP
.EX
gefs# snap main myimmutable
.EE
.PP
To create a new mutable snapshot that does not take automatic
checkpoints:
.IP
.EX
gefs# snap -Sm main mymutable
.EE
.PP
To delete a snapshot:
.IP
.EX
gefs# snap -d mysnap
.EE
.PP
To create a new user:
.IP
.EX
# mount the adm namespace (as a user in adm group):
# and add the user to the user file
% mount /srv/gefs /adm adm
% sam /adm/users

# create the user home directory
# and tmp snapshot
% mount /srv/gefs /n/u %main
% mkdir /n/u/usr/$newuser
% chgrp -u $newuser /n/u/usr/$newuser
% chgrp $newuser /n/u/usr/$newuser
.EE
.SH BUGS
.PP
Currently, it's not possible to change the mutability of a snapshot.
Instead, a new label needs to be created.
.PP
.SH SEE ALSO
.IR gefs (4)