iankelling.org Git - distro-setup/blob - btrbk-run

   1 #!/bin/bash
   2 # Copyright (C) 2016 Ian Kelling
   3
   4 # Licensed under the Apache License, Version 2.0 (the "License");
   5 # you may not use this file except in compliance with the License.
   6 # You may obtain a copy of the License at
   7
   8 #     http://www.apache.org/licenses/LICENSE-2.0
   9
  10 # Unless required by applicable law or agreed to in writing, software
  11 # distributed under the License is distributed on an "AS IS" BASIS,
  12 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13 # See the License for the specific language governing permissions and
  14 # limitations under the License.
  15
  16
  17 # todo: if we cancel in the middle of a btrfs send, then run again
  18 # immediately, the received subvolume doesn't get a Received UUID:
  19 # field, and we won't mount it. Need to figure out a solution that will
  20 # fix this.
  21
  22
  23 [[ $EUID == 0 ]] || exec sudo -E "${BASH_SOURCE[0]}" "$@"
  24
  25 source /usr/local/lib/err
  26
  27 usage() {
  28   cat <<'EOF'
  29 btrbk-run [OPTIONS] [run|resume|archive]
  30 usually -t TARGET_HOST or -s SOURCE_HOST
  31
  32 Note, at source location, intentionally not executable, run and read
  33 install-my-scripts.
  34
  35 EOF
  36   echo "top of script file:"
  37   sed -n '1,/^[# ]*end command line/{p;b};q' "$0"
  38   exit $1
  39 }
  40
  41
  42
  43 script_name="${BASH_SOURCE[0]}"
  44 script_name="${script_name##*/}"
  45 pre="${SSH_CLIENT:+$HOSTNAME} $script_name:"
  46 m() { if $verbose; then printf "$pre%s\n"  "$*"; fi;  "$@"; }
  47 e() { printf "$pre%s\n"  "$*"; }
  48 die() { printf "$pre%s\n" "$*" >&2; echo "exiting with status 1" >&2; exit 1; }
  49 mexit() { echo "$pre: exiting with status $1"; exit $1; }
  50
  51 # latest $MAIL_HOST
  52 if [[ -e /b/bash_unpublished/source-state ]]; then
  53   source /b/bash_unpublished/source-state
  54 fi
  55
  56 # note q is owned by root:1000
  57
  58 mountpoints=()
  59
  60 rsync_mountpoint=/q
  61
  62 ret=0
  63 # default options
  64 conf_only=false
  65 dry_run=false # mostly for testing
  66 rate_limit=no
  67 verbose=true; verbose_arg=-v
  68 if [[ $INVOCATION_ID ]]; then
  69   # INVOCATION_ID means running as a systemd service. we cant show progress in this case,
  70   # but if we pass the arg, it will insert mbuffer into the command.
  71   progress_arg=
  72 else
  73   progress_arg="--progress"
  74 fi
  75 incremental_strict=false
  76 pull_reexec=false
  77
  78 default_args_file=/etc/btrbk-run.conf
  79 if [[ -s $default_args_file ]]; then
  80   # shellcheck disable=SC2046 # we want word splitting
  81   set -- $(< $default_args_file) "$@"
  82   # i havent used this feature yet, so warn about it
  83   echo "$0: warning: default btrbk-run options set in $default_args_file (sleeping 5 seconds):"
  84   cat $default_args_file
  85   sleep 5
  86 fi
  87
  88 targets=()
  89 early=false
  90 cron=false
  91 fast=false
  92 orig_args=("$@")
  93 temp=$(getopt -l cron,fast,pull-reexec,help 23ceil:m:npqrs:t:vh "$@") || usage 1
  94 eval set -- "$temp"
  95 while true; do
  96   case $1 in
  97     # some behaviors specific to running under cron:
  98     # - skip hosts where xprintidle haven't been idle recently
  99     # - if we can't ssh to 1 or more hosts, still do the rest
 100     # - if we aren't MAIL_HOST and no -m or -s, just exit
 101     --cron)
 102       cron=true
 103       pre=
 104       ;;
 105     # for the rare case we want to run multiple instances at the same time
 106     -2) conf_suf=2 ;;
 107     -3) conf_suf=3 ;;
 108     # only creates the config file, does not run btrbk
 109     -c) conf_only=true ;;
 110     # quit early, just btrbk, no extra remounting etc.
 111     -e) early=true ;;
 112     # skip various checks. when we run twice in a row for
 113     # switch mail-host, no need to repeat the same checks again.
 114     --fast) fast=true ;;
 115     -i) incremental_strict=true ;;
 116     # bytes per second, suffix k m g
 117     -l) rate_limit=$2; shift ;;
 118     # Comma separated mountpoints to backup. This has defaults set below.
 119     -m) IFS=, mountpoints=($2); unset IFS; shift ;;
 120     -n) dry_run=true ;;
 121     # hide progress
 122     -p) progress_arg= ;;
 123     # internal option for rerunning under newer SOURCE_HOST version.
 124     --pull-reexec) pull_reexec=true;;
 125     # quiet
 126     -q) verbose=false; verbose_arg=; progress_arg= ;;
 127     # source host to receive a backup from
 128     -s)
 129       source=$2
 130       bbksource=$source
 131       if [[ $source == *:* ]]; then
 132         bbksource="[$source]"
 133       fi
 134       shift
 135       ;;
 136     # target hosts to send to. empty is valid for just doing local
 137     # snapshot. we have default hosts we will populate.
 138     -t) IFS=, targets=($2); unset IFS; shift ;;
 139     # verbose.
 140     -v) verbose=true; verbose_arg=-v ;;
 141     -h|--help) usage ;;
 142     --) shift; break ;;
 143     *) die "Internal error!" ;;
 144   esac
 145   shift
 146 done
 147
 148 cmd_arg=${1:-run}
 149
 150
 151 std_preserve="36h 14d 8w 24m"
 152 q_preserve="18h 14d 8w"
 153
 154 case $cmd_arg in
 155   run|resume) : ;;
 156
 157   # This works better than the normal archive command. We have to
 158   # specify the mount points, but that is what we are used to doing and
 159   # we prefer it. Another difference is that archive works recursively
 160   # and we don't care about that. Sometimes we may still want to run
 161   # btrbk archive, but it doesn't even use the config file, so just
 162   # run it directly, eg:
 163   # time s btrbk -v archive /mnt/r7/amy/boot/btrbk ssh://bo/mnt/boot2/btrbk
 164   archive)
 165     cmd_arg=resume
 166     std_preserve="999h 999d 999w 999m"
 167     q_preserve="$std_preserve"
 168     preserve_arg=-p
 169     ;;
 170   *) die "untested command arg" ;;
 171 esac
 172
 173 if (( $# > 1 )); then
 174   die: "only 1 nonoption arg is supported"
 175 fi
 176
 177 if [[ -v targets && $source ]]; then
 178   # note, this doesnt need to be the case, but
 179   # we would need to think about it.
 180   die "error: -t and -s are mutually exclusive"
 181 fi
 182
 183 if $verbose; then
 184   printf "$pre options: conf_only=%s\ndry_run=%s\nrate_limit=%s\nverbose=%s\ncmd_arg=%s" "$conf_only" "$dry_run" "$rate_limit" "$verbose" "$cmd_arg"
 185 fi
 186 ### end options parsing
 187
 188 # remove path from earlier version of btrbk
 189 rm -f /usr/sbin/btrbk
 190 # note, this still works as intended if there is no /usr/bin/btrbk
 191 if [[ /a/opt/btrbk/btrbk -nt /usr/bin/btrbk ]]; then
 192   if [[ -e /b/distro-functions/src/package-manager-abstractions ]]; then
 193     . /b/distro-functions/src/package-manager-abstractions
 194     pi asciidoctor
 195   fi
 196   cd /a/opt/btrbk
 197   m make install
 198 fi
 199
 200 # TODO: i wonder if there should be an option to send to the default
 201 # targets, plus any given on the command line.
 202
 203
 204
 205 kd_spread=false
 206 # set default targets
 207 if [[ ! -v targets && ! $source ]]; then
 208   if $cron; then
 209     if [[ $HOSTNAME != "$MAIL_HOST" ]]; then
 210       if [[ $HOSTNAME == kd && $MAIL_HOST == x3 ]]; then
 211         if ping -q -c1 -w1 x3.office.fsf.org &>/dev/null; then
 212           work_host=x3.office.fsf.org
 213         elif ping -q -c1 -w1 x3wg.b8.nz &>/dev/null; then
 214           work_host=x3wg.b8.nz
 215         fi
 216         if [[ $work_host ]]; then
 217           source_state="$(ssh $work_host cat /a/bin/bash_unpublished/source-state)"
 218           eval "$source_state"
 219           if [[ $MAIL_HOST == x3 ]]; then
 220             kd_spread=true
 221           else
 222             echo "MAIL_HOST=$MAIL_HOST, nothing to do"
 223             mexit 0
 224           fi
 225         else
 226           echo "MAIL_HOST=$MAIL_HOST, nothing to do"
 227           mexit 0
 228         fi
 229       else
 230         echo "MAIL_HOST=$MAIL_HOST, nothing to do"
 231         mexit 0
 232       fi
 233     fi
 234   fi
 235
 236   at_work=false
 237   at_home=false
 238
 239   case $HOSTNAME in
 240     kw|kd|frodo|x2|x3|sy) : ;;
 241     *)
 242       die "error: no default targets for this host, use -t"
 243       ;;
 244   esac
 245
 246   case $HOSTNAME in
 247     kw)
 248       at_work=true
 249       ;;&
 250     kd|frodo)
 251       at_home=true
 252       ;;&
 253     x2|x3|sy)
 254       if [[ $(dig +short @10.2.0.1 -x 10.2.0.2 2>&1 ||:) == kd.b8.nz. ]] \
 255            && ip n show 10.2.0.1 | grep . &>/dev/null; then
 256         at_home=true
 257       elif ping -q -c1 -w1 hal.office.fsf.org &>/dev/null \
 258           && ip n show 192.168.0.26 | grep . &>/dev/null; then
 259         at_work=true
 260       fi
 261       ;;&
 262     *)
 263       if $at_home; then
 264         if ! $kd_spread; then
 265           # main work machine
 266           if ping -q -c1 -w1 x3.office.fsf.org &>/dev/null; then
 267             targets+=(x3.office.fsf.org)
 268           else
 269             targets+=(x3wg.b8.nz)
 270           fi
 271         fi
 272         for h in frodo kd; do
 273           if [[ $HOSTNAME == "$h" ]]; then
 274             continue
 275           fi
 276           targets+=($h.b8.nz)
 277         done
 278         for h in x2 x3 sy; do
 279           if [[ $HOSTNAME == "$h" ]]; then
 280             continue
 281           fi
 282           if ping -q -c1 -w1 $h.b8.nz &>/dev/null; then
 283             targets+=($h.b8.nz)
 284           elif ping -q -c1 -w1 ${h}w.b8.nz &>/dev/null; then
 285             targets+=(${h}w.b8.nz)
 286           fi
 287         done
 288       elif $at_work; then
 289         if ping -q -c1 -w1 iank.vpn.office.fsf.org &>/dev/null; then
 290           targets+=(iank.vpn.office.fsf.org)
 291         else
 292           targets+=(i.b8.nz)
 293         fi
 294         for h in x2 x3 kw; do
 295           if [[ $HOSTNAME == "$h" ]]; then
 296             continue
 297           fi
 298           if ping -q -c1 -w1 $h.office.fsf.org &>/dev/null; then
 299             targets+=($h.office.fsf.org)
 300           fi
 301         done
 302       else
 303         targets+=(i.b8.nz)
 304       fi
 305       ;;
 306   esac
 307 fi
 308
 309 if [[ -v targets ]]; then
 310   echo "targets: ${targets[*]}"
 311 fi
 312
 313 if [[ $source ]]; then
 314   echo "source: $source"
 315 fi
 316
 317 if [[ ${mountpoints[0]} ]]; then
 318   for mp in ${mountpoints[@]}; do
 319     if [[ -e /nocow/btrfs-stale/$mp ]]; then
 320       die "error: $mp is stale, mount-latest-subvol first"
 321     fi
 322   done
 323 else
 324   # set default mountpoints
 325   if [[ ${targets[0]} == tp ]]; then
 326     prospective_mps=(/a)
 327   else
 328     case $HOSTNAME in
 329       *)
 330         prospective_mps=()
 331         if [[ $source ]]; then
 332           source_state="$(ssh $source cat /a/bin/bash_unpublished/source-state)"
 333           eval "$source_state"
 334           source_host="$(ssh $source cat /etc/hostname)"
 335           if [[ $source_host == "$MAIL_HOST" ]]; then
 336             prospective_mps+=(/o)
 337           fi
 338           if [[ $source_host == "$HOST2" ]]; then
 339             prospective_mps+=(/a /ar /qr /q)
 340           fi
 341         else
 342           if [[ $HOSTNAME == "$MAIL_HOST" ]]; then
 343             prospective_mps+=(/o)
 344           fi
 345           if [[ $HOSTNAME == "$HOST2" ]]; then
 346             prospective_mps+=(/a /ar /qr /q)
 347           fi
 348         fi
 349         # note: put q last just in case its specific retention options were to
 350         # affect other config sections. I havent tested if that is the case.
 351         ;;
 352     esac
 353   fi
 354   for mp in ${prospective_mps[@]}; do # default mountpoints to sync
 355     if [[ -e /nocow/btrfs-stale/$mp ]]; then
 356       e "warning: $mp stale, not adding to default mountpoints"
 357       continue
 358     fi
 359     if awk '{print $2}' /etc/fstab | grep -xF $mp &>/dev/null; then
 360       mountpoints+=($mp)
 361     fi
 362   done
 363 fi
 364
 365 echo "mountpoints: ${mountpoints[*]}"
 366
 367 ##### end command line parsing ########
 368
 369 if ! $fast && [[ $source ]]; then
 370   if [[ $(ssh $source ps --no-headers -o comm 1) == systemd ]]; then
 371     status=$(ssh $source systemctl is-active btrbk.service) || : # normally returns 3
 372     case $status in
 373       inactive|failed) : ;;
 374       *)
 375         echo "$0: error: cron btrbk is running on source. exiting out of caution"
 376         mexit 1
 377     esac
 378   fi
 379 fi
 380
 381 # pull_reexec stops us from getting into an infinite loop if there is some
 382 # kind of weird problem
 383 pulla=false
 384 for m in "${mountpoints[@]}"; do
 385   if [[ $m == /a ]]; then
 386     pulla=true
 387     break
 388   fi
 389 done
 390 if ! $pull_reexec && [[ $source ]] && $pulla ; then
 391   tmpf=$(mktemp)
 392   m rsync -ra $source:/usr/local/bin/{mount-latest-subvol,check-subvol-stale} /usr/local/bin
 393   m rsync -ra $source:/usr/local/lib/err /usr/local/lib
 394   m scp $source:/a/bin/distro-setup/btrbk-run $tmpf
 395   if ! diff -q $tmpf ${BASH_SOURCE[0]}; then
 396     e "found different version on host $source. reexecing"
 397     install -T $tmpf /usr/local/bin/btrbk-run
 398     m /usr/local/bin/btrbk-run --pull-reexec "${orig_args[@]}"
 399     mexit 0
 400   fi
 401 fi
 402
 403
 404 if ! command -v btrbk &>/dev/null; then
 405   die "error: no btrbk binary found"
 406 fi
 407
 408 if ! $fast; then
 409   # if our mountpoints are from stale snapshots,
 410   # it doesn't make sense to do a backup.
 411   m check-subvol-stale ${mountpoints[@]} || die "found stale mountpoints in ${mountpoints[*]}"
 412
 413   # for an initial run, btrbk requires the dir to exist.
 414   mkdir -p /mnt/{root,o}/btrbk
 415 fi
 416 local_zone=$(date +%z)
 417
 418 if [[ $source ]]; then
 419   if $fast; then
 420     zone=$local_zone
 421   else
 422     if ! zone=$(ssh root@$source date +%z); then
 423       if $conf_only; then
 424         echo "$0: warning: failed to ssh to root@$source"
 425       else
 426         die failed to ssh to root@$source
 427       fi
 428     fi
 429     if [[ $zone != "$local_zone" ]]; then
 430       die "error: dont confuse yourself with multiple time zones. $h has different timezone than localhost"
 431     fi
 432   fi
 433 else
 434
 435   sshable=()
 436   sshfail=()
 437   min_idle_ms=$((1000 * 60 * 15))
 438   for h in ${targets[@]}; do
 439     if $fast || $conf_only; then
 440       # Use some typical values in this case
 441       root_size=$(( 1024 * 1024 * 2000 )) #2tb
 442       percent_used=10
 443       zone=$(date +%z)
 444     elif remote_str=$(timeout -s 9 6 ssh root@$h "mkdir -p /mnt/root/btrbk /mnt/o/btrbk && date +%z && df --output=size,pcent / | tail -n1"); then
 445       mapfile -t tmp_array <<<"$remote_str"
 446       zone="${tmp_array[0]}"
 447       IFS=" " read -r root_size percent_used <<<"${tmp_array[1]}"
 448       percent_used=${percent_used%%%}
 449
 450       if (( ${#tmp_array[@]} != 2 )); then
 451         die "error: didnt get 2 lines in test ssh to target $h. investigate"
 452       fi
 453       case $percent_used in
 454         [0-9]|[1-9][0-9]) : ;;
 455         *)
 456           die "error: didnt get percent disk use in test ssh to target $h. investigate"
 457           ;;
 458       esac
 459     else
 460       sshfail+=($h)
 461       continue
 462     fi
 463
 464     # we may be booted into a bootstrap fs or something
 465     min_root_kb=$(( 1024 * 1024 * 200 )) # 200 gb
 466     if (( root_size < min_root_kb )); then
 467       continue
 468     fi
 469
 470     if (( percent_used >= 98 )); then
 471       die "error: filesystem on target $h is $percent_used % full"
 472     fi
 473
 474     # This is a separate ssh because xprintidle can fail and thats ok.
 475     if $cron && idle_ms=$(timeout -s 9 6 ssh $h DISPLAY=:0 xprintidle); then
 476       if (( idle_ms < min_idle_ms )); then
 477
 478         # Ignore this host. i sometimes use a non-main machine for
 479         # testing or web browsing, knowing that everything will be wiped
 480         # by the next backup, but I dont want it to happen as Im using
 481         # it from cronjob.
 482         e "warning: $h: active X session in the last 15 minutes, skipping for now"
 483         continue
 484       fi
 485     fi
 486     sshable+=($h)
 487     if [[ $zone != "$local_zone" ]]; then
 488       die "error: dont confuse yourself with multiple time zones. $h has different timezone than localhost"
 489     fi
 490   done
 491   if [[ ! ${sshable[*]} ]] || { ! $cron && [[ ${sshfail[*]} ]]; }; then
 492     die "failed to ssh to hosts: ${sshfail[*]}"
 493   else
 494     if [[ ${sshfail[*]} ]]; then
 495       ret=1
 496       e "error: failed to ssh to ${sshfail[*]} but continuing with other hosts"
 497     fi
 498     targets=(${sshable[@]})
 499   fi
 500 fi
 501
 502
 503 cat >/etc/btrbk$conf_suf.conf <<EOF
 504 ssh_identity /q/root/h
 505 #ssh_identity /root/.ssh/home
 506
 507 # Just a guess that local7 is a good facility to pick.
 508 # It's a bit odd that the transaction log has to be logged to
 509 # a file or syslog, while other output is sent to std out.
 510 # The man does not mention a way for them to be together, but
 511 # I dunno if setting a log level like warn might also output
 512 # transaction info.
 513 transaction_syslog local7
 514
 515 # trying this out
 516 #stream_compress zstd
 517
 518 # so we only run one at a time
 519 lockfile                   /var/lock/btrbk$conf_suf.lock
 520
 521 # default format of short does not accomidate hourly preservation setting
 522 timestamp_format long-iso
 523
 524 # only make a snapshot if things have changed
 525 snapshot_create onchange
 526 # I could make this different from target_preserve,
 527 # if one disk had less space.
 528 # for now, keeping them equal.
 529 snapshot_preserve $std_preserve
 530 snapshot_preserve_min 2h
 531 snapshot_dir btrbk
 532 # so, total backups = ~58
 533 target_preserve $std_preserve
 534 target_preserve_min 2h
 535
 536 # i tried this when investigating: clone no source subvolume found error
 537 #incremental_prefs sro:1 srn:1 sao san:1 aro:1 arn:1
 538
 539 # if something fails and it's not obvious, try doing
 540 # btrbk -l debug -v dryrun
 541
 542 rate_limit $rate_limit
 543 EOF
 544
 545 if $incremental_strict; then
 546   cat >>/etc/btrbk$conf_suf.conf <<EOF
 547 incremental strict
 548 EOF
 549 fi
 550
 551 qconf() {
 552   case $sub in
 553     q)
 554       # q has sensitive data i dont want to backup for so long
 555       cat >>/etc/btrbk$conf_suf.conf <<EOF
 556 snapshot_preserve $q_preserve
 557 snapshot_preserve_min 2h
 558 snapshot_dir btrbk
 559 target_preserve $q_preserve
 560 target_preserve_min 2h
 561 EOF
 562       ;;
 563   esac
 564
 565 }
 566
 567 # make /q be last
 568 mp_count=${#mountpoints[@]}
 569 for (( i=0; i < mp_count - 1 ; i++ )); do
 570   if [[ ${mountpoints[i]} == /q ]]; then
 571     unset "mountpoints[i]"
 572     mountpoints+=(/q)
 573   fi
 574 done
 575
 576 for m in ${mountpoints[@]}; do
 577   case $m in
 578     /o)
 579       vol=/mnt/o
 580       ;;
 581     *)
 582       vol=/mnt/root
 583       ;;
 584   esac
 585
 586   sub=${m#/}
 587   if [[ $source ]]; then
 588     cat >>/etc/btrbk$conf_suf.conf <<EOF
 589 volume ssh://$bbksource$vol
 590 subvolume $sub
 591 EOF
 592     qconf
 593     cat >>/etc/btrbk$conf_suf.conf <<EOF
 594 target send-receive $vol/btrbk
 595 EOF
 596   fi
 597   if (( ${#targets[@]} )); then
 598     cat >>/etc/btrbk$conf_suf.conf <<EOF
 599 volume $vol
 600 subvolume $sub
 601 EOF
 602     qconf
 603     for tg in ${targets[@]}; do
 604       # handle ipv6
 605       if [[ $tg == *:* ]]; then
 606         tg="[$tg]"
 607       fi
 608       cat >>/etc/btrbk$conf_suf.conf <<EOF
 609 target send-receive ssh://$tg$vol/btrbk
 610 EOF
 611     done
 612   fi
 613 done
 614
 615 # todo: umount first to ensure we don't have any errors
 616 # todo: do some kill fuser stuff to make umount more reliable
 617
 618
 619 if $conf_only; then
 620   mexit 0
 621 fi
 622
 623
 624
 625 if $dry_run; then
 626   m btrbk -c /etc/btrbk$conf_suf.conf -v -n $cmd_arg
 627   mexit 0
 628 fi
 629 # -q and just using the syslog option seemed nice,
 630 # but it doesn't show when a send has a parent and when it doesn't.
 631 m btrbk -c /etc/btrbk$conf_suf.conf $preserve_arg $verbose_arg $progress_arg $cmd_arg
 632
 633 if $early; then
 634   exit 0
 635 fi
 636
 637 # todo: tp not valid anymore.
 638 # if we have it, sync to systems which don't
 639 if mountpoint $rsync_mountpoint >/dev/null; then
 640   for tg in ${targets[@]}; do
 641     case $tg in
 642       tp)
 643         dirs=(/p/c/machine_specific/tp)
 644         for x in /p/c/machine_specific/*.hosts; do
 645           if grep -qxF $tg $x; then
 646             dirs+=(${x%.hosts})
 647           fi
 648         done
 649         m rsync -aSAXPH --specials --devices --delete --relative ${dirs[@]} root@$tg:/
 650         ;;
 651     esac
 652   done
 653 fi
 654
 655 subvols=()
 656 for mp in "${mountpoints[@]}"; do
 657   subvols+=("${mp##*/}")
 658 done
 659 if [[ $source ]]; then
 660   m mount-latest-subvol "${subvols[@]}"
 661 else
 662   m /a/exe/mount-latest-remote ${targets[@]}
 663 fi
 664
 665 if [[ $ret == 0 ]]; then
 666   for tg in ${targets[@]}; do
 667     :
 668     #ssh root@$tg /a/exe/mail-backup-clean
 669   done
 670 fi
 671
 672 mexit $ret
 673
 674 # todo: move variable data we don't care about backing up
 675 # to /nocow and symlink it.
 676
 677
 678 # background on btrbk timezones. with short/long, timestamps use local time.
 679 # for long, if your local time moves backwards, by moving timezones or
 680 # for an hour when daylight savings changes it, you will temporarily get
 681 # a more aggressive retention policy for the overlapping period, and
 682 # vice versa for the opposite timezone move. The alternative is using
 683 # long-iso, which puts timezone info into the timestamp, which means
 684 # that instead of shifting time, you shift the start of day/week/month
 685 # which is used for retention to your new local time, which means for
 686 # example, if you moved forward by 8 hours, the daily/weekly/monthly
 687 # retention will be 8 hours more aggressive since midnight is at a new
 688 # time, unless you fake the timzeone using the TZ env variable.
 689 # However, in the short term, there will be no inconsistencies.
 690 # I don't see any problem with shifting when the day starts for
 691 # retention, so I'm using long-iso.
 692
 693 # note to create a long-iso timestamp: date +%Y%m%dT%H%M%S%z