CV0-004 Troubleshooting — All Questions With Answers

Refer to the exhibit.

```
$ ping 10.0.1.10
PING 10.0.1.10 (10.0.1.10) 56(84) bytes of data.
From 10.0.0.1 icmp_seq=1 Destination Host Unreachable
From 10.0.0.1 icmp_seq=2 Destination Host Unreachable
```

Refer to the exhibit.

```
$ iptables -L -n -v
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0            state INVALID
  123  4567 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0            state ESTABLISHED,RELATED
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:22

Chain FORWARD (policy DROP 0 packets, 0 bytes)
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
```

Refer to the exhibit.

```
$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        20G   18G  1.5G  93% /
/dev/sdb1       100G   20G   80G  20% /data
```

Refer to the exhibit.

```
$ ping 10.10.10.10
PING 10.10.10.10 (10.10.10.10) 56(84) bytes of data.
From 10.10.10.1 icmp_seq=1 Destination Host Unreachable
From 10.10.10.1 icmp_seq=2 Destination Host Unreachable
From 10.10.10.1 icmp_seq=3 Destination Host Unreachable

--- 10.10.10.10 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2003ms

$ traceroute 10.10.10.10
traceroute to 10.10.10.10 (10.10.10.10), 30 hops max, 60 byte packets
 1  10.10.10.1  0.433 ms  0.428 ms  0.414 ms
 2  * * *
 3  * * *
 4  * * *
```

Refer to the exhibit.

Filesystem      Size  Used Avail Use% Mounted on
/dev/xvda1      20G   19G  1.0G  95% /
tmpfs           1.9G   0   1.9G   0% /dev/shm

Application error: 'No space left on device' when writing to /var/log/app.log.

Refer to the exhibit.

VPC Flow Logs excerpt:
2 123456789010 eni-12345678 10.0.1.5 10.0.2.10 12345 80 6 1500 100 1625082000 1625082060 ACCEPT OK
2 123456789010 eni-12345678 10.0.1.5 10.0.2.10 12346 80 6 1500 200 1625082061 1625082121 ACCEPT OK
2 123456789010 eni-12345678 10.0.1.5 10.0.2.10 12347 80 6 100 0 1625082122 1625082182 REJECT OK

iptables -L -v -n
Chain INPUT (policy ACCEPT)
 pkts bytes target     prot opt in     out     source               destination
    0     0 DROP       tcp  --  eth0   *       0.0.0.0/0            10.0.1.10  tcp dpt:22
    5   600 ACCEPT     tcp  --  eth0   *       10.0.0.0/16          10.0.1.10  tcp dpt:22

error log: 
[ERROR] azcopy: failed to perform copy command: 
The request failed due to: 
Server failed to authenticate the request. 
Make sure the value of Authorization header is formed correctly 
including the signature.

CloudWatch Logs:
2025-03-01T10:00:00Z ERROR: Connection refused to database endpoint: db.example.com:3306
2025-03-01T10:00:01Z INFO: Retrying in 1 second...
2025-03-01T10:00:02Z ERROR: Connection refused to database endpoint: db.example.com:3306

Refer to the exhibit.

```
$ sudo systemctl status nginx
● nginx.service - A high performance web server and a reverse proxy server
   Loaded: loaded (/usr/lib/systemd/system/nginx.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Mon 2024-03-25 10:23:45 UTC; 1min 30s ago
  Process: 12345 ExecStart=/usr/sbin/nginx (code=exited, status=1/FAILURE)
 Main PID: 12345 (code=exited, status=1/FAILURE)
   CGroup: /system.slice/nginx.service

Mar 25 10:23:45 web01 systemd[1]: Starting nginx...
Mar 25 10:23:45 web01 nginx[12345]: nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
Mar 25 10:23:45 web01 nginx[12345]: nginx: [emerg] still could not bind()
```

Refer to the exhibit.

[cloud-init] Error: Failed to mount /dev/xvdb1 on /mnt: No such device
[cloud-init] Failed to mount /dev/xvdb1 on /mnt: No such device
[cloud-init] Instance initialization failed: mountall