RHCSA9 dump-3

6. cron

On ServerB, schedule a cron job that prints "Break Time!" every two hours on weekdays on your current screen. Use the root user as the user performing the cron job.

answere)

• crontab -e

00 */2 * * 1-5 echo "Break Time!"

*/2: 매 2시간마다
1-5: weekdays

validation

• crontab -l

---

8. shell

On ServerB, change the user sam's login shell to Bash.

answere)

• vi /etc/passwd

sam:x:1001:1001::/home/sam:/bin/bash

validation

• su - sam
• echo $SHELL

---

13. bash shell

On ServerB, write a script /sum.sh that prompts the user to enter two integers and then displays their sum.

answere)

• cd /
• touch sum.sh
• chmod +x sum.sh
• vi /sum.sh

#!/bin/bash

(( SUM=$1+$2 ))
echo "sum is: $SUM"

(( )): bash의 산술 계산 전용 구문

validation

• ./sum.sh 1 2

---

23. sed

Which of the following commands replaces each occurrence of 'sam' in the file letter with 'Sam' and writes the result to the file newletter?

answere)

• sed s/sam/Sam/g letter > newletter
man sed
s/regexp/replacement: regex에 해당하면, replacement로 교체
  g: global

validation

• vi letter

sam juwon test sam

• sed 's/sam/Sam/g' ltter > newletter
• cat newletter

---

30. hardware clock

Which command is used to sync the hardware clock to the system clock? (Specify ONLY the command without any path or parameters.)

answere)

• hwclock

validation

• hwclock
• timedatectl

---

35. thin pool, thin provisioned volume

On ServerB, using disk /dev/sdb, complete the following tasks:

• Create a 5T thin provisioned volume named mythinvol under a 2G thin pool called mythinpool within a 4G volume group named myvg.
• Extend the size of mythinpool by 1G.
• Rename the thin pool from mythinpool to thinpool1.
• Rename the thin provisioned volume from mythinvol to thinvol1.

answere)

• lsblk
• fdisk /dev/sdb
• n
  new
• Enter
  select partition(primary / secondary)
• Enter
  partiton number
• Enter
  first sector
• +4G
  size
• t
  type change
• 8e
  Linux LVM
• w
  write
• lsblk

create thinpool

• pvcreate /dev/sdb1
• vgcreate myvg /dev/sdb1
• lvcreate -L 2G --thinpool mythinpool /dev/myvg
• lvs
  Attr 행에서, 맨앞에 t로 시작하는 것 확인 가능

create thin provisioned volume

• lvcreate -V 5T --name mythinvol /dev/myvg/mythinpool
-V: Virtual size
• lvs
  Attr 행에서, 맨앞에 V로 시작하는 것 확인 가능

extend thinpool

• lvextend -L +1G /dev/myvg/mythinpool
• lvs

rename thin pool

• lvrename /dev/myvg/mythinpool /dev/myvg/mythinpool1
• lvs

rename thin provisioned volume

• lvrename /dev/myvg/mythinvol /dev/myvg/mythinvol1
• lvs

---

36. nfs, autofs

On ServerB, configure autofs to automatically mount user directories from the remote NFS ServerA. The server exports the /nfs/home directory, which contains individual user directories (e.g., /nfs/home/tom).

Mount these user directories on demand under the local /nfs/users directory. Ensure the mount is accessible and persists across reboots.

answere)
ServerA - nfs server

• dnf install -y nfs-utils
• systemctl enable --now nfs-server rpcbind

• firewall-cmd --list-all
• firewall-cmd --add-service=nfs --permanent
• firewall-cmd --add-service=rpc-bind --permanent
• firewall-cmd --add-service=mountd --permanent
• firewall-cmd --reload
• firewall-cmd --list-all

• mkdir -p /nfs/home/tom
• vi /etc/exports

/nfs/home serverb(no_root_squash,rw,sync)

• exportfs -arv
• showmount -e
• systemctl restart nfs-server

ServerB - nfs client, autofs

• dnf install -y nfs-utils

• showmount -e servera
• mkdir -p /nfs/users
• vi /etc/auto.master

/nfs/users	/etc/auto.nfs

• vi /etc/auto.nfs

*	-fstype=nfs,rw,sync		servera:/nfs/home/&

*: /nfs/users/*를 의미함.
&: 매칭되는 값을 그대로 대체한다는 것을 의미

• systemctl restart autofs

validation

• cd /nfs/users/tom
• df -Th

---

37. mbr dd

Which of the following commands overwrites the bootloader located on /dev/sda without overwriting the partition table or any data following it?

answere)

• dd if=/dev/zero of=/dev/sda bs=440 count=1
man dd
  MBR(첫 512바이트) 구조: 0–439(=440바이트): 부트스트랩 코드(bootloader code)

---

38. find

On ServerB, write a script named /find_rf.sh that prints out a list of files owned by root and with the SUID bit set in /usr.

answere)

• cd /
• touch find_rf.sh
• chmod +x find_rf.sh

#!/bin/bash
find /usr -uid 0 -perm -4000

man find
-perm 4000: SetUID
-perm 2000: SetGID
-perm 1000: Sticky

• ./find_rf.sh

validation

• cd /usr
• ls -al

---

0. umask

Configure the system so that when user sam creates files and directories, the following default permissions are applied:

• Files: rw- --- ---
• Directories: rwx --- ---

answere)

• vi /home/sam/.bash_profile

umask=077

file은 원래 기본적으로 x권한이 빠진다.

validation

• touch test1
• mkdir test2