RHCSA-B1. 破解修改root密码

Posted 2021-10-19 白-胖-子

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红帽RHCE考试上午-RHCSA（RH134）

serverb.example.com 任务

1. 改root密码

第二部分的题如果破不了密码则进不去系统，则考试就挂了

任务要求

将serverb 的root 密码设置为123 。
您需要获得系统访问权限才能进行此操作开机

完成步骤

导航页面按e 键 -> linux 行尾加rd.break console=tty0 -> ctrl x
mount -o rw,remount /sysroot
chroot /sysroot
echo 123 | passwd --stdin root touch
touch /.autorelabel
## 若系统之前开启了selinux，则必须执行该命令，否则将无法重启重置（这一步很关键！）
sync

考察的知识点：

mount 挂载

救援模式中的根是假根，真根在/sysroot
需要重新挂载上才能进行读写操作
-o remount：将一个已经挂下的档案系统重新用不同的方式挂上。例如原先是唯读的系统，现在用可读写的模式重新挂上。
-o rw：用可读写模式挂上。

touch /.autorelabel

.autorelabel 作用是让系统重新进行扫描所有文件。当selinux关闭的时候，可以不建立该文件；但selinux开启时，必须建立！

sync

强制将内存中的文件缓冲写入磁盘，更新块信息。

CentOS 启动过程总结

POST
boot loader centos7是grub2
vmlinux(initramfs.img)
roofs
/sbin/init
/etc/inittab 设置默认运行级别
/etc/rc.d/rc.sysinit 运行系统初始脚本完成系统初始化
/etc/rc#.d/Sxxxx 启动需要启动服务关闭对应下需要关闭的服务
/etc/rc.d/rc.local
设置登录终端

CentOS 7之后版本引导顺序

UEFi或Bios初始化，运行POST开机自检
选择启动设备
引导装载程序, centos7是grub2,加载装载程序的配置文件：

/etc/grub.d/
/etc/default/grub
/boot/grub2/grub.cfg

加载initramfs驱动模块
加载内核选项
内核初始化，centos7使用systemd代替init
执行initrd.target所有单元，包括挂载/etc/fstab
从initramfs根文件系统切换到磁盘根目录
systemd执行默认target配置，配置文件/etc/systemd/system/default.target
systemd执行sysinit.target初始化系统及basic.target准备操作系统
systemd启动multi-user.target下的本机与服务器服务
systemd执行multi-user.target下的/etc/rc.d/rc.local
Systemd执行multi-user.target下的getty.target及登录服务
systemd执行graphical需要的服务

Linux的bootloader

LILO：LInux LOader，早期的bootloader，功能单一
GRUB: GRand Unified Bootloader, CentOS 5,6 GRUB 0.97: GRUB Legacy， CentOS 7 以后使用GRUB 2.02

GRUB 启动阶段

primary boot loader :
1st stage：MBR的前446个字节
1.5 stage：MBR 之后的扇区，让stage1中的bootloader能识别stage2所在的分区上的文件系统
secondary boot loader ：2nd stage，分区文件/boot/grub/

GURB主要内容

[root@C8-4-184-nfs ~]# ll /etc/grub.d/
total 84
-rwxr-xr-x. 1 root root  8958 Nov 26  2019 00_header
-rwxr-xr-x. 1 root root  1043 Jun 27  2019 00_tuned
-rwxr-xr-x. 1 root root  1240 Nov 26  2019 01_menu_auto_hide
-rwxr-xr-x. 1 root root   232 Nov 26  2019 01_users
-rwxr-xr-x. 1 root root 13434 Nov 26  2019 10_linux
-rwxr-xr-x. 1 root root 11696 Nov 26  2019 20_linux_xen
-rwxr-xr-x. 1 root root  2559 Nov 26  2019 20_ppc_terminfo
-rwxr-xr-x. 1 root root 10670 Nov 26  2019 30_os-prober
-rwxr-xr-x. 1 root root  1412 Nov 26  2019 30_uefi-firmware
-rwxr-xr-x. 1 root root   214 Nov 26  2019 40_custom
-rwxr-xr-x. 1 root root   216 Nov 26  2019 41_custom
-rw-r--r--. 1 root root   483 Nov 26  2019 README
[root@C8-4-184-nfs ~]# ll /etc/default/grub
-rw-r--r-- 1 root root 350 May 20 06:28 /etc/default/grub
[root@C8-4-184-nfs ~]# cat /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="net.ifnames=0 crashkernel=auto resume=UUID=b3fd1c68-6653-41ff-8ecb-25fdcfeeced9 rhgb quiet net.ifnames=0 net.ifnames=0"
GRUB_DISABLE_RECOVERY="true"
GRUB_ENABLE_BLSCFG=true
[root@C8-4-184-nfs ~]# cat /etc/grub
grub2.cfg  grub.d/    
[root@C8-4-184-nfs ~]# cat /etc/grub2.cfg 
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub2-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
set pager=1

if [ -f ${config_directory}/grubenv ]; then
  load_env -f ${config_directory}/grubenv
elif [ -s $prefix/grubenv ]; then
  load_env
fi
if [ "${next_entry}" ] ; then
   set default="${next_entry}"
   set next_entry=
   save_env next_entry
   set boot_once=true
else
   set default="${saved_entry}"
fi

if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
else
  menuentry_id_option=""
fi

export menuentry_id_option

if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function load_video {
  if [ x$feature_all_video_module = xy ]; then
    insmod all_video
  else
    insmod efi_gop
    insmod efi_uga
    insmod ieee1275_fb
    insmod vbe
    insmod vga
    insmod video_bochs
    insmod video_cirrus
  fi
}

terminal_output console
if [ x$feature_timeout_style = xy ] ; then
  set timeout_style=menu
  set timeout=5
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
  set timeout=5
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/00_tuned ###
set tuned_params=""
set tuned_initrd=""
### END /etc/grub.d/00_tuned ###

### BEGIN /etc/grub.d/01_menu_auto_hide ###
if [ "${boot_success}" = "1" -o "${boot_indeterminate}" = "1" ]; then
  set last_boot_ok=1
else
  set last_boot_ok=0
fi

# Reset boot_indeterminate after a successful boot
if [ "${boot_success}" = "1" ] ; then
  set boot_indeterminate=0
# Avoid boot_indeterminate causing the menu to be hidden more then once
elif [ "${boot_indeterminate}" = "1" ]; then
  set boot_indeterminate=2
fi
set boot_success=0
save_env boot_success boot_indeterminate

if [ x$feature_timeout_style = xy ] ; then
  if [ "${menu_show_once}" ]; then
    unset menu_show_once
    save_env menu_show_once
    set timeout_style=menu
    set timeout=60
  elif [ "${menu_auto_hide}" -a "${last_boot_ok}" = "1" ]; then
    set orig_timeout_style=${timeout_style}
    set orig_timeout=${timeout}
    if [ "${fastboot}" = "1" ]; then
      # timeout_style=menu + timeout=0 avoids the countdown code keypress check
      set timeout_style=menu
      set timeout=0
    else
      set timeout_style=hidden
      set timeout=1
    fi
  fi
fi
### END /etc/grub.d/01_menu_auto_hide ###

### BEGIN /etc/grub.d/01_users ###
if [ -f ${prefix}/user.cfg ]; then
  source ${prefix}/user.cfg
  if [ -n "${GRUB2_PASSWORD}" ]; then
    set superusers="root"
    export superusers
    password_pbkdf2 root ${GRUB2_PASSWORD}
  fi
fi
### END /etc/grub.d/01_users ###

### BEGIN /etc/grub.d/10_linux ###
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 --hint='hd0,msdos1'  ea560777-7040-46e1-9931-633142400896
else
  search --no-floppy --fs-uuid --set=root ea560777-7040-46e1-9931-633142400896
fi
insmod part_msdos
insmod ext2
set boot='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=boot --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 --hint='hd0,msdos1'  ea560777-7040-46e1-9931-633142400896
else
  search --no-floppy --fs-uuid --set=boot ea560777-7040-46e1-9931-633142400896
fi

# This section was generated by a script. Do not modify the generated file - all changes
# will be lost the next time file is regenerated. Instead edit the BootLoaderSpec files.
#
# The blscfg command parses the BootLoaderSpec files stored in /boot/loader/entries and
# populates the boot menu. Please refer to the Boot Loader Specification documentation
# for the files format: https://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/.

set default_kernelopts="root=UUID=827b1562-fd3a-4e03-ad8b-f4c0b8def517 ro net.ifnames=0 crashkernel=auto resume=UUID=b3fd1c68-6653-41ff-8ecb-25fdcfeeced9 rhgb quiet net.ifnames=0 net.ifnames=0 "

insmod blscfg
blscfg
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/20_ppc_terminfo ###
### END /etc/grub.d/20_ppc_terminfo ###

### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/30_uefi-firmware ###
### END /etc/grub.d/30_uefi-firmware ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  ${config_directory}/custom.cfg ]; then
  source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###
[root@C8-4-184-nfs ~]# cat /boot/grub2/grub.cfg 
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub2-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
set pager=1

if [ -f ${config_directory}/grubenv ]; then
  load_env -f ${config_directory}/grubenv
elif [ -s $prefix/grubenv ]; then
  load_env
fi
if [ "${next_entry}" ] ; then
   set default="${next_entry}"
   set next_entry=
   save_env next_entry
   set boot_once=true
else
   set default="${saved_entry}"
fi

if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
else
  menuentry_id_option=""
fi

export menuentry_id_option

if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function load_video {
  if [ x$feature_all_video_module = xy ]; then
    insmod all_video
  else
    insmod efi_gop
    insmod efi_uga
    insmod ieee1275_fb
    insmod vbe
    insmod vga
    insmod video_bochs
    insmod video_cirrus
  fi
}

terminal_output console
if [ x$feature_timeout_style = xy ] ; then
  set timeout_style=menu
  set timeout=5
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
  set timeout=5
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/00_tuned ###
set tuned_params=""
set tuned_initrd=""
### END /etc/grub.d/00_tuned ###

### BEGIN /etc/grub.d/01_menu_auto_hide ###
if [ "${boot_success}" = "1" -o "${boot_indeterminate}" = "1" ]; then
  set last_boot_ok=1
else
  set last_boot_ok=0
fi

# Reset boot_indeterminate after a successful boot
if [ "${boot_success}" = "1" ] ; then
  set boot_indeterminate=0
# Avoid boot_indeterminate causing the menu to be hidden more then once
elif [ "${boot_indeterminate}" = "1" ]; then
  set boot_indeterminate=2
fi
set boot_success=0
save_env boot_success boot_indeterminate

if [ x$feature_timeout_style = xy ] ; then
  if [ "${menu_show_once}" ]; then
    unset menu_show_once
    save_env menu_show_once
    set timeout_style=menu
    set timeout=60
  elif [ "${menu_auto_hide}" -a "${last_boot_ok}" = "1" ]; then
    set orig_timeout_style=${timeout_style}
    set orig_timeout=${timeout}
    if [ "${fastboot}" = "1" ]; then
      # timeout_style=menu + timeout=0 avoids the countdown code keypress check
      set timeout_style=menu
      set timeout=0
    else
      set timeout_style=hidden
      set timeout=1
    fi
  fi
fi
### END /etc/grub.d/01_menu_auto_hide ###

### BEGIN /etc/grub.d/01_users ###
if [ -f ${prefix}/user.cfg ]; then
  source ${prefix}/user.cfg
  if [ -n "${GRUB2_PASSWORD}" ]; then
    set superusers="root"
    export superusers
    password_pbkdf2 root ${GRUB2_PASSWORD}
  fi
fi
### END /etc/grub.d/01_users ###

### BEGIN /etc/grub.d/10_linux ###
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 --hint='hd0,msdos1'  ea560777-7040-46e1-9931-633142400896
else
  search --no-floppy --fs-uuid --set=root ea560777-7040-46e1-9931-633142400896
fi
insmod part_msdos
insmod ext2
set boot='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=boot --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 --hint='hd0,msdos1'  ea560777-7040-46e1-9931-633142400896
else
  search --no-floppy --fs-uuid --set=boot ea560777-7040-46e1-9931-633142400896
fi

# This section was generated by a script. Do not modify the generated file - all changes
# will be lost the next time file is regenerated. Instead edit the BootLoaderSpec files.
#
# The blscfg command parses the BootLoaderSpec files stored in /boot/loader/entries and
# populates the boot menu. Please refer to the Boot Loader Specification documentation
# for the files format: https://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/.

set default_kernelopts="root=UUID=827b1562-fd3a-4e03-ad8b-f4c0b8def517 ro net.ifnames=0 crashkernel=auto resume=UUID=b3fd1c68-6653-41ff-8ecb-25fdcfeeced9 rhgb quiet net.ifnames=0 net.ifnames=0 "

insmod blscfg
blscfg
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/20_ppc_terminfo ###
### END /etc/grub.d/20_ppc_terminfo ###

### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/30_uefi-firmware ###
### END /etc/grub.d/30_uefi-firmware ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  ${config_directory}/custom.cfg ]; then
  source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

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