ASCII(American Standard Code for Information Interchange,美国信息交换标准代码),是最早产生的编码规范,共128个字符,用7位二进制表示(00000000-01111111即0x00-0x7F),可以看出ASCII码只需要1个字节的存储空间,它没有特定的编码方式,直接使用地址对应的二进制数来表示,非要说那就叫他ASCII 编码方式。可以表示阿拉伯数字和大小写英文字母,以及一些简单的符号。
(类)Unix系统,拓展名可有可无,有file命令,这个命令可以告诉我们文件到底是什么格式文件拓展名不是文件格式的本质区别,内容才是。把a.zip改成a.txt/a.jgp/a.mp3,无论什么文件名,file都让其原形毕露:Zip archive data, at least v1.0 to extract。file命令的工作原理可这篇文章。
# systemd-analyzecritical-chain
The timeafter the unit is active or started is printed after the "@"character.
The time the unit takes tostartis printed after the "+"character.
multi-user.target @20.222s
└─mariadb.service @11.657s +8.565s
......
systemctl list-unit-files 列出所有可用单元
# systemctl list-unit-files
UNIT FILE STATE
proc-sys-fs-binfmt_misc.automount static
.....
systemctl list-units 列出所有运行中单元
# systemctl list-units
UNIT LOAD ACTIVE SUB DESCRIPTION
proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File Syste
evices-pl...erial8250-tty-ttyS2.device loaded active plugged
...
systemctl list-units 列出所有失败单元
UNIT LOAD ACTIVE SUB DESCRIPTION
kdump.service loaded failedfailed Crash recovery kernel arming
...
$ cat /var/log/vboxadd-setup.log
Building the main Guest Additions 6.0.12moduleforkernel 4.18.0-80.7.1.el8_0.x86_64.
Error building the module. Buildoutputfollows.
make V=1 CONFIG_MODULE_SIG= -C /lib/modules/4.18.0-80.7.1.el8_0.x86_64/build M=/tmp/vbox.0 SRCROOT=/tmp/vbox.0 -j1 modules
Makefile:958: *** "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel". Stop.
make: *** [/tmp/vbox.0/Makefile-footer.gmk:111: vboxguest] Error 2
Could not find the X.Org or XFree86 Window System, skipping.
modprobe vboxguest failed