Scheduled tasks are scheduled to be executed at once

At a specified time point, perform a one-time task

Depends on the atd service and needs to be started to implement the at task

The at queue is stored in the /var/spool/at directory

-V: Display version information

-l: List the jobs waiting to be run in the specified queue; equivalent to atq

-d: Delete the specified job; equivalent to atrm

-c: View specific job tasks

<span class="token namespace">[root@localhost ~]</span><span class="token comment"># systemctl start atd</span>
<span class="token namespace">[root@localhost ~]</span><span class="token comment"># systemctl enable atd</span>
<span class="token namespace">[root@localhost ~]</span><span class="token comment"># at now +1min</span>
at> useradd xwz
at><span class="token comment"># Ctrl+D結(jié)束</span>
job 1 at Thu Aug 27 15:35:00 2020
<span class="token namespace">[root@localhost ~]</span><span class="token comment"># atq</span>
1 Thu Aug 27 15:35:00 2020 a root
<span class="token namespace">[root@localhost ~]</span><span class="token comment"># id xwz</span>
uid=1000<span class="token punctuation">(</span>xwz<span class="token punctuation">)</span> gid=1000<span class="token punctuation">(</span>xwz<span class="token punctuation">)</span> 組=1000<span class="token punctuation">(</span>xwz<span class="token punctuation">)</span>

Whitelist: /etc/at.allow does not exist by default. Only users in this file can execute the at command

Blacklist: /etc/at.deny exists by default. Users in this file are denied the ability to execute at commands, while users not in the at.deny file can execute them

If both files do not exist, only root can execute the at command

Cycle scheduling execution cron user level

<span class="token namespace">[root@localhost ~]</span><span class="token comment"># systemctl start crond</span>
<span class="token namespace">[root@localhost ~]</span><span class="token comment"># systemctl enable crond</span>
crond 進(jìn)程每分鐘會(huì)處理一次計(jì)劃任務(wù)
<span class="token namespace">[root@localhost ~]</span><span class="token comment"># ls /var/spool/cron # 儲(chǔ)存位置</span>

<span class="token punctuation">[</span>root@localhost ~<span class="token punctuation">]</span><span class="token comment"># crontab -l # 列出當(dāng)前用戶所有計(jì)劃任務(wù)</span>
<span class="token punctuation">[</span>root@localhost ~<span class="token punctuation">]</span><span class="token comment"># crontab -r # 刪除當(dāng)前用戶計(jì)劃任務(wù)</span>
<span class="token punctuation">[</span>root@localhost ~<span class="token punctuation">]</span><span class="token comment"># crontab -e # 編輯當(dāng)前用戶計(jì)劃任務(wù)</span>

Time-sharing sun and moon worship commands

Basics of Log Management

rsyslogd: Most of the log records are related to system operations. Applications such as secure US Linux hosts, authentication sshd, su, scheduled tasks at, cronhttpd/nginx/mysql, etc. can record logs in their own way

tail/var/log/messages system main log file

tail-f/var/log/messages dynamically view the tail of the log file

tail/var/log/croncrond, the log generated by the at process

wCurrently logged in user/var/log/wtmp

tail/var/log/mysqld.logMySQL

<span class="token namespace">[root@localhost ~]</span><span class="token comment"># rpm -qc rsyslog</span>
<span class="token operator">/</span>etc<span class="token operator">/</span>logrotate<span class="token punctuation">.</span>d<span class="token operator">/</span>syslog <span class="token comment"># 日志輪轉(zhuǎn)(切割)相關(guān)</span>
<span class="token operator">/</span>etc<span class="token operator">/</span>rsyslog<span class="token punctuation">.</span>conf <span class="token comment"># rsyslogd的主配置文件</span>
<span class="token operator">/</span>etc<span class="token operator">/</span>sysconfig<span class="token operator">/</span>rsyslog <span class="token comment"># rsyslogd相關(guān)文件</span>

Log service name

cron(LOG_CRON) Log formed by system scheduled tasks cront and at

daemon(LOG_DAEMON) Logs related to each daemon process

ftp(LOG_FTP)Log generated by ftp daemon

syslog(LOG_SYSLOG) stores the log information generated by the syslogd service (even though the service name has been changed to reyslogdlinux installation, and many configurations still inherit the syslogd service, so the service name is not changed here)

logrotateLog rotation

logrotate就是拿來進(jìn)行日志輪替（也叫日志輪詢）的，也就是把舊的日志文件聯(lián)通并更名linux 計(jì)劃任務(wù)沒執(zhí)行，同時(shí)創(chuàng)建一個(gè)新的空日志文件拿來記錄新日志，當(dāng)舊日志文件超出保存的范圍時(shí)就刪掉。

注：針對(duì)任何日志文件(rsyslog日志、Nginx訪問或錯(cuò)誤日志)

logrotate本身不是系統(tǒng)守護(hù)進(jìn)程linux 計(jì)劃任務(wù)沒執(zhí)行，它是通過計(jì)劃任務(wù)crond每晚執(zhí)行

<span class="token namespace">[root@localhost ~]</span><span class="token comment"># cat /etc/cron.daily/logrotate</span>

主配置文件

<span class="token punctuation">[</span>root@localhost ~<span class="token punctuation">]</span><span class="token comment"># vim /etc/logrotate.conf</span>
weekly <span class="token comment"># 一周輪轉(zhuǎn)一次</span>
rotate <span class="token number">4</span> <span class="token comment"># 保留4份日志，也就是說,如果進(jìn)行了5次日志輪替，就會(huì)刪除第一個(gè)備份日志</span>
create <span class="token comment"># 主動(dòng)創(chuàng)建新的日志文件</span>
dateext <span class="token comment"># 使用日期來作為文件名的后綴</span>
<span class="token comment">#compress # 每次輪轉(zhuǎn)需不需要進(jìn)行壓縮</span>
include /etc/logrotate.d <span class="token comment"># 導(dǎo)入其他應(yīng)用的日志輪轉(zhuǎn)規(guī)則</span>
/var/log/wtmp <span class="token punctuation">{</span> <span class="token comment"># 以下參數(shù)僅對(duì)此目錄有效</span>
monthly <span class="token comment"># 一個(gè)月輪轉(zhuǎn)一次</span>
create 0664 root utmp <span class="token comment"># 輪轉(zhuǎn)后創(chuàng)建新文件，并設(shè)置權(quán)限</span>
minsize 1M <span class="token comment"># 最小達(dá)到1M才會(huì)輪轉(zhuǎn)</span>
rotate <span class="token number">1</span> <span class="token comment"># 僅保留一個(gè)日志備份。也就是只保留wtmp和wtmp.1日志</span>
<span class="token punctuation">}</span>
/var/log/btmp <span class="token punctuation">{</span>
missingok <span class="token comment"># 如果日志不存在,則忽略該日志的警告信息</span>
monthly
create 0600 root utmp
rotate <span class="token number">1</span>
<span class="token punctuation">}</span>

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