# RH342 Flashcards

Quick Q&A format. Cover the answer column to test yourself.

## Logs

| Question | Answer |
|----------|--------|
| View current boot logs | `journalctl -b` |
| View logs for httpd service | `journalctl -u httpd` |
| Follow logs live | `journalctl -f` |
| View kernel messages | `journalctl -k` or `dmesg` |
| Search SELinux denials | `ausearch -m avc -ts today` |
| Enable persistent journal | `mkdir /var/log/journal`, set `Storage=persistent` |
| Security log location | `/var/log/secure` |
| General syslog location | `/var/log/messages` |

## Boot/GRUB

| Question | Answer |
|----------|--------|
| Show default kernel | `grubby --default-kernel` |
| Set default kernel | `grubby --set-default /boot/vmlinuz-xxx` |
| List all boot entries | `grubby --info=ALL` |
| Add kernel argument | `grubby --update-kernel=ALL --args="xxx"` |
| GRUB config (BIOS) | `/boot/grub2/grub.cfg` |
| GRUB config (UEFI) | `/boot/efi/EFI/redhat/grub.cfg` |
| Regenerate GRUB (BIOS) | `grub2-mkconfig -o /boot/grub2/grub.cfg` |
| Boot to rescue mode | `systemd.unit=rescue.target` |
| Break to initramfs | `rd.break` |
| List UEFI boot entries | `efibootmgr` |

## Hardware

| Question | Answer |
|----------|--------|
| CPU info | `lscpu` |
| Memory info | `dmidecode -t memory` |
| Kernel messages | `dmesg -T` |
| PCI devices | `lspci` |
| USB devices | `lsusb` |
| SCSI/storage devices | `lsscsi` |
| Hardware error summary | `ras-mc-ctl --summary` |

## Storage

| Question | Answer |
|----------|--------|
| List LVs | `lvs` |
| List VGs | `vgs` |
| List PVs | `pvs` |
| Extend LV by 5G | `lvextend -L +5G /dev/vg/lv` |
| Repair XFS | `xfs_repair /dev/xxx` (unmount first) |
| List block devices | `lsblk -f` |
| Check disk scheduler | `cat /sys/block/sda/queue/scheduler` |
| Device mapper list | `dmsetup ls` |
| Wipe disk signatures | `wipefs --all /dev/xxx` |
| Create Stratis pool | `stratis pool create name /dev/xxx` |

## Network

| Question | Answer |
|----------|--------|
| List connections | `nmcli connection show` |
| List devices | `nmcli device status` |
| Bring up connection | `nmcli connection up "name"` |
| Show listening ports | `ss -tuln` |
| Show ports with processes | `ss -tunlp` |
| List firewall rules | `firewall-cmd --list-all` |
| Add firewall service | `firewall-cmd --add-service=http --permanent` |
| Reload firewall | `firewall-cmd --reload` |
| Scan network for hosts | `nmap -sn 192.168.1.0/24` |
| Show IP addresses | `ip addr show` |

## SELinux

| Question | Answer |
|----------|--------|
| Check mode | `getenforce` |
| Set permissive (temp) | `setenforce 0` |
| Set enforcing (temp) | `setenforce 1` |
| Search AVC denials | `ausearch -m avc -ts recent` |
| View file context | `ls -Z /path` |
| Add file context rule | `semanage fcontext -a -t type_t '/path(/.*)?'` |
| Apply contexts | `restorecon -Rv /path` |
| Add port label | `semanage port -a -t type_t -p tcp port` |
| Set boolean (persistent) | `setsebool -P boolname on` |
| List booleans | `getsebool -a` |
| Analyze denial | `sealert -a /var/log/audit/audit.log` |
| Force relabel | `touch /.autorelabel && reboot` |
| Web content type | `httpd_sys_content_t` |

## Kdump

| Question | Answer |
|----------|--------|
| Check kdump status | `kdumpctl status` |
| Show reserved memory | `kdumpctl showmem` |
| Crash dump location | `/var/crash/` |
| Kdump config file | `/etc/kdump.conf` |
| Kernel param for kdump | `crashkernel=auto` |
| Enable SysRq | `echo 1 > /proc/sys/kernel/sysrq` |
| Trigger test crash | `echo c > /proc/sysrq-trigger` |
| Panic on OOM | `vm.panic_on_oom=1` in sysctl.conf |
| Analyze vmcore | `crash vmlinux vmcore` |
| Quick crash info file | `vmcore-dmesg.txt` |

## Common File Paths

| What | Path |
|------|------|
| GRUB defaults | `/etc/default/grub` |
| Kdump config | `/etc/kdump.conf` |
| SELinux config | `/etc/selinux/config` |
| rsyslog config | `/etc/rsyslog.conf` |
| Journal config | `/etc/systemd/journald.conf` |
| Audit log | `/var/log/audit/audit.log` |
| Crash dumps | `/var/crash/` |
| Persistent journal | `/var/log/journal/` |

## Troubleshooting Checklist

| Issue | First Commands |
|-------|----------------|
| Service won't start | `systemctl status svc`, `journalctl -u svc` |
| SELinux denial | `ausearch -m avc -ts recent`, `ls -Z` |
| Boot failure | Boot previous kernel, `grubby --info=ALL` |
| Network unreachable | `ip addr`, `ping gateway`, `firewall-cmd --list-all` |
| Disk full | `df -h`, `df -i`, `du -sh /*` |
| Permission denied | Check `ls -l`, then `ls -Z` for SELinux |
| Kernel crash | Check `/var/crash/`, analyze `vmcore-dmesg.txt` |