文件操作 - 50-motd-news

文件: /etc/update-motd.d/50-motd-news

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#!/bin/sh
#
#    50-motd-news - print the live news from the Ubuntu wire
#    Copyright (C) 2016-2020 Canonical Ltd.
#    Copyright (C) 2016-2017 Dustin Kirkland
#
#    Authors: Dustin Kirkland <kirkland@canonical.com>
#             Steve Langasek <steve.langasek@canonical.com>
#
#    This program is free software; you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation; either version 2 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License along
#    with this program; if not, write to the Free Software Foundation, Inc.,
#    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

##############################################################################
# This program could be rewritten in C or Golang for faster performance.
# Or it could be rewritten in Python or another higher level language
# for more modularity.
# However, I've insisted on shell here for transparency!
#                                                                     - Dustin
##############################################################################

# Source the local configuration
[ -r /etc/default/motd-news ] && . /etc/default/motd-news

# Exit immediately, unless we're enabled
# This makes this script very easy to disable in /etc/default/motd-news configuration
[ "$ENABLED" = "1" ] || exit 0

# Ensure sane defaults
[ -n "$URLS" ] || URLS="https://motd.ubuntu.com"
[ -n "$WAIT" ] || WAIT=5
[ -n "$CACHE" ] || CACHE="/var/cache/motd-news"
[ "$1" = "--force" ] && FORCED=1

# Ensure we print safely, maximum of the first 10 lines,
# maximum of the first 80 chars per line, no control chars
safe_print() {
	cat "$1" | head -n 10 | tr -d '\000-\011\013\014\016-\037' | cut -c -80
}

# If we're not forcing an update, and we have a cached motd-news file,
# then just print it and exit as quickly as possible, for login performance.
# Note that systemd should keep this cache file up to date, asynchronously
if [ "$FORCED" != "1" ]; then
  	if [ -r $CACHE ]; then
		echo
		safe_print $CACHE
	elif [ "$(id -u)" -eq 0 ]; then
		: > $CACHE
	fi
	exit 0
fi

# If we've made it here, we've been given the --force argument,
# probably from the systemd motd-news.service.  Let's update...

# Abort early if wget is missing
[ -x /usr/bin/wget ] || exit 0

# Generate our temp files, clean up when done
NEWS=$(mktemp) || exit 1
ERR=$(mktemp) || exit 1
CLOUD=$(mktemp) || exit 1
trap "rm -f $NEWS $ERR $CLOUD" HUP INT QUIT ILL TRAP KILL BUS TERM

# Construct a user agent, similar to Firefox/Chrome/Safari/IE to
# ensure a proper, tailored, accurate message of the day

# wget browser version, for debug purposes
wget_ver="$(dpkg -l wget | awk '$1 == "ii" { print($3); exit(0); }')"

# Distribution version, for messages releated to this Ubuntu release
. /etc/lsb-release
lsb=$(echo "$DISTRIB_DESCRIPTION" | sed -e "s/ /\//g")
codename="$DISTRIB_CODENAME"

# Kernel version and CPU type, for messages related to a particular revision or hardware
platform="$(uname -o)/$(uname -r)/$(uname -m)"
arch="$(uname -m)"
cpu="$(grep -m1 "^model name" /proc/cpuinfo | sed -e "s/.*: //" -e "s:\s\+:/:g")"
cloud_id="unknown"
if [ -x /usr/bin/cloud-id ]; then
    /usr/bin/cloud-id > "$CLOUD" 2>/dev/null
    if [ "$?" -eq "0" ]; then
        # sanitize it a bit, just in case
        cloud_id=$(cut -c -40 "${CLOUD}" | tr -c -d '[:alnum:]')
        if [ -z "${cloud_id}" ]; then
            cloud_id="unknown"
        fi
    fi
fi

# Piece together the user agent
USER_AGENT="wget/$wget_ver $lsb $platform $cpu cloud_id/$cloud_id"

# Loop over any configured URLs
for u in $URLS; do
	# Ensure https:// protocol, for security reasons
	case $u in
		https://*)
			true
		;;
		https://motd.ubuntu.com)
			u="$u/$codename/$arch"
		;;
		*)
			continue
		;;
	esac
	# If we're forced, set the wait to much higher (1 minute)
	[ "$FORCED" = "1" ] && WAIT=60
	# Fetch and print the news motd
	result=0
	not_found_is_ok=0
	wget --timeout "$WAIT" -U "$USER_AGENT" -O- --content-on-error "$u" >"$NEWS" 2>"$ERR" || result=$?
	# from wget's manpage: 8   Server issued an error response.
	if [ $result -eq 8 ]; then
		if grep -q "ERROR 404" "$ERR"; then
			# The server's 404 document is the generic, non cloud-specific, motd-news
			# content present in the index.txt file
			not_found_is_ok=1
		fi
	fi
	if [ $result -eq 0 ] || [ $not_found_is_ok -eq 1 ]; then
		echo
		# At most, 10 lines of text, remove control characters, print at most 80 characters per line
		safe_print "$NEWS"
		# Try to update the cache
		safe_print "$NEWS" 2>/dev/null >$CACHE || true
	else
		: > "$CACHE"
 	fi
done
rm -f "$NEWS" "$ERR" "$CLOUD"
exit 0

文件操作 - 50-motd-news

文件: /etc/update-motd.d/50-motd-news

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