在ssh登录服务器时显示服务器信息

在使用 ssh 登录 Linux 时发现会输出系统的统计信息，如：

其中的第一行是在 /etc/motd 文件中定义的，这个文件会在用户登录成功后显示；第二行是在 /etc/motd.d/cockpit 文件中，这是 Cockpit Web 控制台的提示信息；之后的信息都是动态生成的，生成的脚本在 /etc/profile.d/system-info.sh，一些发行版会包含这个文件，内容如下：

#/bin/bash
#Copyright (c) [2019] Huawei Technologies Co., Ltd.
#generic-release is licensed under the Mulan PSL v2.
#You can use this software according to the terms and conditions of the Mulan PSL v2.
#You may obtain a copy of Mulan PSL v2 at:
#     http://license.coscl.org.cn/MulanPSL2
#THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND, EITHER EXPRESS OR
#IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT, MERCHANTABILITY OR FIT FOR A PARTICULAR
#PURPOSE.
#See the Mulan PSL v2 for more details.

# Welcome
welcome=$(uname -r)

# Memory
memory_total=$(free -m | awk 'NR==2 { printf($2)}')
if [ $memory_total -gt 0 ]
then
    memory_usage=$(free -m | awk 'NR==2 { printf("%3.1f%%", $3/$2*100)}')
else
    memory_usage=0.0%
fi

# Swap memory
swap_total=$(free -m | awk 'NR==3 { printf($2)}')
if [ $swap_total -gt 0 ]
then
    swap_mem=$(free -m | awk 'NR==3 { printf("%3.1f%%", $3/$2*100)}')
else
    swap_mem=0.0%
fi

# Usage
usageof=$(df -h / | awk '/\// {print $(NF-1)}')

# System load
load_average=$(awk '{print $1}' /proc/loadavg)

# WHO I AM
whoiam=$(whoami)

# Time
time_cur=$(date)

# Processes
processes=$(ps aux | wc -l)

# Users
user_num=$(users | wc -w)

# Ip address
ip_pre=""
if [ -x "/sbin/ip" ]
then
            ip_pre=$(/sbin/ip a | grep inet | grep -v "127.0.0.1" | grep -v inet6 | awk '{print $2}')
fi

echo -e "\n"
echo -e "Welcome to $welcome\n"
echo -e "System information as of time: \t\t$time_cur\n"
echo -e "System load: \t\t\033[0;33;40m$load_average\033[0m"
echo -e "Processes: \t\t$processes"
echo -e "Memory used: \t\t$memory_usage"
echo -e "Swap used: \t\t$swap_mem"
echo -e "Usage On: \t\t$usageof"

for line in $ip_pre
do
            ip_address=${line%/*}
            echo -e "IP address: \t\t$ip_address"
done
echo -e "Users online: \t\t$user_num"
if [ "$whoiam" == "root" ]
then
        echo -e "\n"
else
        echo -e "To run a command as administrator(user \"root\"),use \"sudo <command>\"."
fi

那么为什么这个脚本会执行呢，它在 /etc/profile 文件中被调用，它遍历了 /etc/profile.d 文件夹下的所有 shell 脚本，并检测文件是否可读：

for i in /etc/profile.d/*.sh /etc/profile.d/sh.local ; do
    if [ -r "$i" ]; then
        if [ "${-#*i}" != "$-" ]; then
            . "$i"
        else
            . "$i" >/dev/null
        fi
    fi
done

在用户登录时，系统会自动执行 /etc/profile 文件，这个文件包含全局的 shell 设置，适用于所有用户。