Master Comptia-Linux+ Troubleshooting with our interactive study cards designed for effective learning. These flashcards use proven spaced repetition techniques to help you memorize key concepts, definitions, and facts. Perfect for students, professionals, and lifelong learners seeking to improve knowledge retention and ace exams through active recall practice.
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Identify the problem by gathering information and understanding symptoms
dmesg or journalctl for systemd systems
/var/log/ directory
/var/log/syslog or /var/log/messages depending on distribution
/var/log/auth.log or /var/log/secure
journalctl
journalctl -u servicename
tail -f /var/log/logfile or journalctl -f
df -h to show disk usage by filesystem
du -sh * or find / -type f -size +100M
Disk is full or inode limit reached
df -i
free -h or cat /proc/meminfo
High swap usage or OOM (Out of Memory) killer messages
Kernel process that terminates processes when system runs out of memory
top or htop
Load average significantly higher than number of CPU cores
Terminated process that hasn't been cleaned up by parent
ps aux | grep Z or look for <defunct> in process list
ping hostname or IP address
ip addr show or ifconfig
nslookup domain or dig domain
ip route show or route -n
traceroute hostname or tracepath hostname
Interface shows "DOWN" in ip link show output
ip link set interfacename up or ifup interfacename
netstat -tulpn or ss -tulpn
Service is not running on target port or firewall blocking
Network routing issue or firewall blocking at network level
systemctl status servicename or ps aux | grep servicename
Configuration errors missing dependencies or port conflicts
systemctl status servicename or journalctl -xe
Many services have configtest option or service-specific validation commands
lsof or lsof -p PID
lsof -i :portnumber or netstat -tulpn | grep portnumber
Input/output errors or fsck errors during boot
fsck /dev/devicename (filesystem must be unmounted)
Troubleshooting and recovery with minimal services running
Add "single" or "1" to kernel parameters at boot
Minimal environment for system recovery similar to single-user mode
dmesg or journalctl -b
Errors in dmesg about device failures or SMART errors
smartctl -a /dev/devicename (requires smartmontools)
systemctl --failed
Permission denied errors in logs or command output
Check file ownership with ls -l and verify user group memberships
ausearch -m avc or grep AVC /var/log/audit/audit.log
setenforce 0 (sets to permissive mode)
Library not found or "cannot open shared object file" errors
ldd /path/to/binary
ldconfig
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