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Interview Prep > Technical - Linux/OS > Flashcards

Technical - Linux/OS Flashcards

1
Q

Hard vs Soft/Sym Link (+how to create)

A

Hard Link:
Definition: Filesystem entry pointing directly to the inode of a file.
Deletion Behavior: No problem
Creation: ln <source></source> <target></target>

Soft/Symbolic Link:
Definition: File system entry that creates a new inode that references the path to the target file.
Deletion Behavior: Broken link
Creation: ln -s <source></source> <target></target>

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2
Q

File Descriptor (Explain stdout, stderr, and stdin)

A

Definition: An integer that uniquely identifies an open file in a process.

Standard Descriptors:
stdin (0): Standard input.
stdout (1): Standard output.
stdout (2): Standard error.

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3
Q

Process vs Thread

A

Process:
Definition: An independent program in execution, with its own memory space.
Resource Sharing: None, separate memory space and resources.

Thread:
Definition: A smaller unit of execution within a process.
Resource Sharing: Separate registers and stack, but shares memory space.

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4
Q

Linux Boot Process (BIOS > MBR > GRUB/LILO > Kernel > Init System)

A

BIOS: Initializes hardware, loads and executes bootloader from MBR (Master boot record).
GRUB/LILO: Bootloader(GRUB) loads and executes the Linux kernel and mounts initial RAM disk
Kernel: Initializes system hardware and mounts the root filesystem.
Init System: Starts user-space processes (e.g., systemd, SysVinit).

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5
Q

Full Disk Encryption LUKS (TPM Integration)**

A

LUKS: Linux Unified Key Setup; provides full disk encryption.
TPM: Trusted Platform Module; stores encryption keys securely.
Integration: LUKS can be used with TPM to protect encryption keys against tampering.

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6
Q

Secure Boot

A

Purpose: Ensures that only signed and authorized software is loaded during boot.
Mechanism: Checks digital signatures of bootloaders and kernels to prevent unauthorized modifications.

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7
Q

Inode (How to check inode number and inode usage)

A

Index Node:
Definition: Data structure containing metadata about a file (e.g., size, permissions), but not file name or contents.
Check: ls -i <file> shows the inode number. df -i shows inode usage.</file>

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8
Q

Zombie Process

A

Definition: A process that has completed execution but still has an entry in the process table.
Cause: Parent process has not yet read the exit status.
Check: ps aux | grep Z

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9
Q

Iptables vs UFW**

A

Definition: User-space utility for configuring Linux kernel firewall.
Usage: iptables -A INPUT -p tcp –dport 22 -j ACCEPT (Allow SSH)

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10
Q

DF vs DU

A

DF: Shows filesystem disk space usage.
Command: df -h
DU: Shows disk usage of files and directories.
Command: du -sh <directory></directory>

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11
Q

SELinux**

A

Definition: Security-Enhanced Linux; provides mandatory access controls.
Commands:
Check Status: sestatus
Manage Policies: semanage, setenforce

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12
Q

How to check disk space, memory, cpu, and io

A

Disk Space: df -h
Memory: free -h
CPU: top or htop
IO: iostat (requires sysstat package)

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13
Q

How to check open files (+why significant)

A

Command: lsof
Significance: Identifies files and sockets opened by processes, useful for troubleshooting and security.

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14
Q

How to check open ports on local system

A

netstat -tuln

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15
Q

How to scan external system for open ports (+flags)

A

nmap -p <port-range> <target></target></port-range>

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16
Q

Systemd (How to create, status, stop, start)

A

Create Service: Write a .service file in /etc/systemd/system/
Status: systemctl status <service>
Start: systemctl start <service>
Stop: systemctl stop <service></service></service></service>

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17
Q

How to trace a network path from source to target

A

traceroute <destination></destination>

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18
Q

How to lookup IP for DNS record and reverse

A

DNS Record: dig <domain> or nslookup <domain>
Reverse Lookup: dig -x <IP> or nslookup <IP></IP></IP></domain></domain>

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19
Q

Linux Filesystem Architecture

A

Standard Dirs:
/root - home dir for root user
/bin - essential user command binaries
/boot - static files of boot loader
/dev - rep hardware devices
/etc - system-wide config
/home - user home dirs
/lib - shared libraries and kernel modules
/media - mount point for removable media
/mnt - mount point for temp mounted fs
/sbin - system bins
/srv - data for system services
/opt - add-on optional application pkgs
/root - Home dir for root user
/tmp - temporary fs
/usr - user-related programs
/var - variable data files w/frequent change

Special FSs:
/proc - virtual fs providing process and kernel info
/sys - virtual fs providing info and control over kernels devices and modules
/dev/shm - Temp file storage for inter-process comms

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20
Q

Linux Kernel Architecture**

A

Monolithic Kernel: A single large kernel that includes the core functionalities and all device drivers.

System Call Interface: Provides the interface between user-space applications and kernel services.

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21
Q

How to configure basic LAN:

A

Use netplan or ip commands to configure interface, addresses, gateway, and nameservers.

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22
Q

How to check running processes (+how to kill)

A

Running Processes: ps aux or top
Kill Process: kill <PID> or kill -9 <PID> (force kill)</PID></PID>

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23
Q

/proc**

A
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24
Q

/sys**

A
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25
Q

/dev/shm**

A
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26
Q

Linux Namespaces

27
Q

Linux Control Groups (cGroups)

28
Q

AppArmour

29
Q

RAM Disk

30
Q

strace

31
Q

Linux Families/Distros (3)

A
  1. Debian: Ubuntu, Mint
  2. Fedora: RHEL, CentOS
  3. SUSE: SLES, OpenSUSE
32
Q

Linux vs Unix

33
Q

Initialization Systems (SystemD vs InitD vs SystemV)

35
Q

whatis vs apropos

36
Q

man vs info

37
Q

grep vs egrep (grep “” <>)

38
Q

How to count words or lines in a file

39
Q

Redirection:
1. Redirect stdout to file
2. Redirect stderr to file
3. Redirect stdout/stderr to file
4. Redirect stdout to file AND print
5. Redirect stderr to file AND print
6. Redirect stdout/stderr to file AND print
7. Overwrite vs append for both ways
8. Which operators will create file

40
Q

Permissions:
1. What are the symbolic characters for users, operations, and permissions?
2. What are the octal numbers for permissions

A
  1. ugoa +_= rwx
  2. x=1, w=2, r=4
41
Q

umask (what, how to set)

42
Q

Compression vs archive (w/tar + gz & bz2)

43
Q

journalctl (unit, grep, boot logs, config)

44
Q

nice/renice

46
Q

pgrep/pkill

47
Q

sysVinit, upstart, and systemd

48
Q

Tuned

49
Q

Fdisk vs gdisk vs parted

50
Q

Swap (what is it and basic steps to setup RHEL vs Ubuntu)

51
Q

Steps to format and mount block device persistently.

52
Q

List block devices and check partitions

53
Q

xfs vs ext4 vs vfat vs ntfs

54
Q

Brace expansion (list, range)

55
Q

Paramater expansion (default use, default assign, substring, replace)

56
Q

autofs and nfs/smb

57
Q

setgid, setuid, and sticky bit

59
Q

at vs chrony

60
Q

Background jobs, shell job table, and SIGHUP:
1. command &
2. nohup command &
3. ctrl-z
4. jobs
5. bg %<id>
6. fg %<id>
7. disown %<id></id></id></id>

61
Q

useradd, usermod, userdel, groupadd, groupmod, groupdel, passwd, chage

62
Q

How to enforce password policies in Linux?

63
Q

How to view and update firewall config:
1. ufw
2. firewalld/firewall-cmd

64
Q

ACL:
1. setfacl
2. getfacl

Interview Prep (14 decks)

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