Written by: Robert R. Russell on Monday, August 17, 2020.
TIK, formerly The Imperator Knight,
makes long-form videos about lesser know WW2 battles. The early actions in the
North African Campaign are exciting. I have one of his documentary playlists
embedded below.
Written by: Robert R. Russell on Friday, August 14, 2020.
Now that I can read and write a snapshot, how do I process a list of snapshots
in a useful manner? First, let me define what I mean by a useful manner. I want
the tool to keep a copy of all automatic snapshot on the source ZFS tree on the
destination tree as an automatic snapshot is aged off of the source it needs
to be aged off of the destination as well. It will transfer snapshots one at
a time instead of transferring all of the intermediate snapshots at the same
time; the ZFS send -i option versus the -I option.
The best data structure for this is a tree or graph. The tree starts with a
list of yearly snapshots. Every snapshot has two slices of children—one for the
child frequency snapshots older than it. The younger slice will be populated
only if the current snapshot is the youngest child at its frequency strata.
A picture demonstrating my idea follows this paragraph. I will delve into
implementation details in the next part of the ZFS Backup Tool series.
Written by: Robert R. Russell on Thursday, August 13, 2020.
Now that I can read a list of snapshots, I need to read a snapshot and transfer
it to the destination. The three functions that allow me to do that are
exec.StdinPipe(),
exec.StdoutPipe(),
and io.CopyBuffer().
The process consists of the following steps:
Create an exec.Cmd representing the zfs send command
Use exec.StdoutPipe() to connect a pipe to the output of the command
created in step 1.
Create an exec.Cmd representing the zfs receive command
Use exec.StdinPipe() to connect a pipe to the input of the command created
in step 3.
Start both commands
Use io.CopyBuffer() to read from the snapshot to the receiver.
Written by: Robert R. Russell on Monday, August 10, 2020.
When I rebooted my blog, yet again, I gave myself the personal challenge of
writing at least one article per day. Except for August 3rd, 2020, I have met
that challenge. Let’s see it continues.
Written by: Robert R. Russell on Sunday, August 9, 2020.
Which software to use?
With the ZFS backup tool, I want to host the code for it here on my website
instead of GitHub. What options are available? If I want to host the bare repo,
I can use ssh for write access and add a virtual host for apache so you can
have read access. If I want a nice web interface, though, I need a different
setup.
A bit of online searching shows four major self-hosted Git web frontends. They
are GitLab, Gitea,
GitBucket, and Gogs.
GitLab and GitBucket are out because they require a lot of extra software to
support the service. GitLab could almost qualify as its own Linux distro with
a bit more work. GitBucket is nearly as bad. That leaves the two clones, Gogs
and Gitea. Gitea is a fork of Gogs with more maintainers. The increase in
maintainers gives Gitea a faster issue resolution, so I chose it.
System requirements
Gitea has very moderate system requirements. Golang, about 256MB of RAM,
and optionally MariaDB, MySQL, or PostgreSQL. An external database is a
recommendation for large sites. I will use MariaDB because I am already using
it and have a working scheduled backup of my entire database server.
Written by: Robert R. Russell on Saturday, August 8, 2020.
Mustie1 does small
engine repair videos. Most of his videos start with something simple that
someone overlooked with the “dead” engine. He fixes that and usually cleans the
engine as well.
Here are three videos where he fixed a forklift that someone abandoned because
two previous mechanics wouldn’t follow their troubleshooting workflow to the
end.
Written by: Robert R. Russell on Friday, August 7, 2020.
Welcome to Part 4 of my series on my tool for backing up ZFS Snapshots to an
external device. In this part, I am discussing how to exec a command and read
its output.
To deal with external commands in Go, you use
the os/exec package. The
primary pieces of the package that I need for now are
exec.Command() and
CombinedOutput().
exec.Command() sets up the Command structure with the command and any
arguments that I am passing to it.
var listCommand = exec.Command("zfs", "list", "-Hrt", "snapshot", "dpool")
That code creates a variable called listCommand, which is ready to run
the command zfs with the arguments list, -Hrt, and snapshot as individual
arguments.
var snapList, err = listCommand.CombinedOutput()
That line of code runs the command I previously prepared, puts both its
Standard Output and Standard Error in a slice of bytes. If the command exited
with an error code other than 0, CombinedOutput sets err to a non-nil value.
snapList will have the Standard Error of the executed command, so printing
snapList’s contents will be useful for debugging.
var snapScanner = bufio.NewScanner(bytes.NewReader(snapList))
if err != nil {
fmt.Println(listCommand)
fmt.Println("Error trying to list snapshots:", err.Error())
for snapScanner.Scan() {
fmt.Println(snapScanner.Text())
}
}
I will need to use the more complicated IO redirection tools provided in the
os/exec package for the zfs send and zfs receive commands. However, for a test
run today, I can use a modification of the loop I used to print the output from
zfs if it errored.
for snapScanner.Scan() {
if snapshotLineRegex.MatchString(snapScanner.Text()) {
var temp = strings.SplitN(snapScanner.Text(), "\t", 2)
var snapshot = ParseSnapshot(temp[0])
if snapshot != nil {
fmt.Println("I found snapshot", snapshot.Name(), "at", snapshot.Path())
}
}
}
}
Written by: Robert R. Russell on Thursday, August 6, 2020.
Today’s project is parsing a snapshot into a custom datatype that gives us
more accessible options to manipulate snapshots. First, the regular expression
strings need to be moved into separate files so I can reference them across
other files.
The essential parts of a snapshot are:
the pool name
the filesystem tree
the Interval
the TimeStamp
To parse a snapshot out of a string.
Confirm that the string matches our regular expression for snapshots and only
contains the regular expression for a snapshot.
If it does not return an error otherwise continue
Split the input string into the path and the snapshot name
Parse the snapshot name into the interval and timestamp fields
Split the path into the pool name and any filesystem tree portions.
Below is a function that implements the listed requirements.
/*
ParseSnapshot parses a string into a Snapshot.
It returns nil on error.
*/funcParseSnapshot(input string) *Snapshot {
var snapshotOnly, err = regexp.Compile("^" + PoolNameRegex + "@" + ZfsSnapshotNameRegex + "$")
if err != nil {
returnnil }
if !snapshotOnly.MatchString(input) {
returnnil }
var snapshotPieces []string = snapshotOnly.FindStringSubmatch(input)
var theSnapshot = Snapshot{}
theSnapshot.Interval = intervalStringToUInt(snapshotPieces[1])
var year, month, day, hour, minute int year, err = strconv.Atoi(snapshotPieces[2])
if err != nil {
returnnil }
month, err = strconv.Atoi(snapshotPieces[3])
if err != nil {
returnnil }
day, err = strconv.Atoi(snapshotPieces[4])
if err != nil {
returnnil }
hour, err = strconv.Atoi(snapshotPieces[5])
if err != nil {
returnnil }
minute, err = strconv.Atoi(snapshotPieces[6])
if err != nil {
returnnil }
theSnapshot.TimeStamp = time.Date(year, time.Month(month), day, hour, minute, 0, 0, time.UTC)
var splitInput []string = strings.Split(input, "@")
iflen(splitInput) != 2 {
returnnil }
var paths []string = strings.Split(splitInput[0], "/")
theSnapshot.pool = paths[0]
iflen(paths) > 1 {
copy(theSnapshot.fsTree, paths[1:])
}
return &theSnapshot
}
funcintervalStringToUInt(input string) uint64 {
switch input {
case"yearly":
return 0
case"monthly":
return 1
case"weekly":
return 2
case"daily":
return 3
case"hourly":
return 4
}
return 5
}
Now that I can create a Snapshot structure I need some utility methods for them.
Read the pool snapshot and file system tree as a single string.
Compare two snapshots by date and interval
Get the snapshot name
Get the full snapshot string. <path>@<snapshot name>
The following code will implement those utility methods.
/*
Path returns a string containing the path of the snapshot
*/func (s Snapshot) Path() string {
var temp strings.Builder
temp.WriteString(s.pool)
iflen(s.fsTree) > 0 {
for _, v := range s.fsTree {
temp.WriteString("/" + v)
}
}
return temp.String()
}
/*
Name returns a string containing the full name of snapshot
*/func (s Snapshot) Name() string {
var temp strings.Builder
temp.WriteString("zfs-auto-snap_")
temp.WriteString(intervalUIntToString(s.Interval) + "-")
fmt.Fprintf(&temp, "%d-%d-%d-%d%d", s.TimeStamp.Year(), s.TimeStamp.Month(), s.TimeStamp.Day(), s.TimeStamp.Hour(), s.TimeStamp.Minute())
return temp.String()
}
funcintervalUIntToString(x uint64) string {
switch x {
case 0:
return"yearly"case 1:
return"monthly"case 2:
return"weekly"case 3:
return"daily"case 4:
return"hourly" }
return"frequent"}
/*
String returns a string equal to s.Path() + "@" + s.Name() for Snapshot s
*/func (s Snapshot) String() string {
return s.Path() + "@" + s.Name()
}
/*
CompareSnapshotDates returns -2 if x occured before y and would include y in its interval
returns -1 if x occured before y
returns 0 if x and y are the same snapshot
returns +1 if y occured after x
err is non nill if the snapshots do not have the same path
*/funcCompareSnapshotDates(x Snapshot, y Snapshot) (int, error) {
if x.Path() != y.Path() {
return 0, errors.New("Can only compare snapshots with the same path")
}
if x.Interval == y.Interval {
if x.TimeStamp.Equal(y.TimeStamp) {
return 0, nil }
if x.TimeStamp.Before(y.TimeStamp) {
return -1, nil }
return 1, nil }
if x.Interval < y.Interval { // y is from a more frequent backup interval than x
var interval time.Time
switch x.Interval {
case 0:
interval = x.TimeStamp.AddDate(-1, 0, 0)
case 1:
interval = x.TimeStamp.AddDate(0, -1, 0)
case 2:
interval = x.TimeStamp.AddDate(0, 0, -7)
case 3:
interval = x.TimeStamp.AddDate(0, 0, -1)
case 4:
interval = x.TimeStamp.Add(time.Hour * -1)
case 5:
interval = x.TimeStamp.Add(time.Minute * -15)
}
if x.TimeStamp.Before(y.TimeStamp) {
return 1, nil }
if interval.Before(y.TimeStamp) {
return -2, nil }
return -1, nil }
// y is from a less frequent backup interval than x
if x.TimeStamp.Before(y.TimeStamp) {
return -1, nil }
if x.TimeStamp.After(y.TimeStamp) {
return 1, nil }
return 0, nil}
You can get the entire source code for the tool below.