These five tools collectively provide simple log–based client–server
replica management. The shell scripts described in replica(1)
provide a more polished interface.
Both client and server maintain textual databases of file system
metadata. Each line is of the form|
Later entries for a path supersede previous ones. A line with
the string REMOVED in the mode field annuls all previous entries
for that path. The entries in a file are typically kept sorted
by path but need not be. These properties facilitate updating
the database atomically by appending to it. Compactdb reads in
database and writes out an equivalent one, sorted by path and
without outdated or annulled records.
A replica is further described on the server by a textual log
listing creation and deletion of files and changes to file contents
and metadata. Each line is of the form:
path mode uid gid mtime length|
The time and gen fields are both decimal numbers, providing an
ordering for log entries so that incremental tools need not process
the whole log each time they are run. The verb, a single character,
describes the event: addition of a file (a), deletion of a file
(d), a change to a file's contents (c), or a change to a file's
metadata (m). Path is the file path on the client; serverpath
the path on the server (these are different when the optional
fifth field in a proto file line is given; see proto(2)). Mode,
uid, gid, and mtime are the files metadata as in the Dir structure
(see stat(5)). For deletion events, the metadata is that of the
For other events, the metadata is that after the event.
Updatedb scans the file system rooted at root for changes not
present in db, noting them by appending new entries to the database
and by writing log events to standard output. The –c option causes
updatedb to consider only file and metadata changes, ignoring
file additions and deletions. By default, the log events
have time set to the current system time and use incrementing
gen numbers starting at 0. The –t option can be used to specify
a different time and starting number. If the –u option is given,
all database entries and log events will use uid rather than the
actual uids. The –x option (which may be specified multiple
times) excludes the named path and all its children from the scan.
If the –l option is given, the database is not changed and the
time and gen fields are omitted from the log events; the resulting
output is intended to be a human–readable summary of file system
activity since the last scan.
Applylog is used to propagate changes from server to client. It
applies the changes listed in a log (read from standard input)
to the file system rooted at clientroot, copying files when necessary
from the file system rooted at serverroot. By default, applylog
does not attempt to set the uid on files; the –u flag enables
this. Applylog will not overwrite local changes made to replicated
files. When it detects such conflicts, by default it prints an
error describing the conflict and takes no action. If the –c flag
is given, applylog still takes no action for files beginning with
the given names, but does so silently and will not report the
in the future. (The conflict is resolved in favor of the client.)
The –s is similar but causes applylog to overwrite the local changes.
(The conflict is resolved in favor of the server.)
Applychanges is, in some sense, the opposite of applylog; it scans
the client file system for changes, and applies those changes
to the server file system. Applychanges will not overwrite remote
changes made to replicated files. For example, if a file is copied
from server to client and subsequently changed on both
server and client, applychanges will not copy the client's new
version to the server, because the server also has a new version.
Applychanges and applylog detect the same conflicts; to resolve
conflicts reported by applychanges, invoke applylog with the –c
or –s flags.
Cphist was designed to copy a dump faithfully from one file server
to the next. Unlike other replica tools it takes special precautions
to ensure that whenever files on the server and oldserver share
a qid.path, the client's corresponding file will be modified and
whenever they do not, the client's file will be deleted and
a copy made from server. Thus the Qid–relationship between the
file on server and oldserver will be the same as for the current
file on the client and that file in the client's most recent dump.
Also, muid is set to preserve the output of history(1). The –e
flag toggles exiting on first error. The default is to exit on
error. The –l lineno sets the first line of the log (the gen field)
to be processed while –v sets verbose output and –n prints what
cphist would do, but does nothing.
time gen verb path serverpath mode uid gid mtime length|