The JUK universal Screw Terminal Block series has the typical features which are decisive for practical applications:
l The universal foot allows the terminal blocks to be easily snapped onto the NS35 or NS32 DIN Rail with G shape.
l Closed screw guide holes ensure screwdriver operation perfect.
l For terminal block with different wire cross-sectional areas, complete accessories are available, such as end plates, partition plates, etc.
l Potential distribution achieved by fixed bridges in the terminal center or insertion bridges in the clamping space.
l Same shape and pitch Grounding Terminal Blocks as the JUK universal series.
l Adopt ZB marker strip system,achieve unified identification.
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Summary of 33 tips for common troubleshooting and processing of Linux operation and maintenance
As a Linux system administrator, it's common to face various issues and failures during daily operations. The key is to accumulate experience, identify problems, analyze their root causes, and continuously improve. Every technological breakthrough comes with challenges, but through persistence and practice, we gain valuable insights that enrich our skills.
The following are some of the common issues I've encountered during my projects, along with their solutions. I hope they resonate with you and help in your troubleshooting journey.
### Common Problem-Solving Highlights
1. **Shell Script Not Executing**
A colleague had an issue where his shell script wouldn't run and showed an error: `: bad interpreter: No such file or directory`. Upon checking, I realized he had written the script on Windows and uploaded it to Linux. The line endings were different (CRLF vs. LF).
**Solution**: Either rewrite the script under Linux or use `vi` to replace the `\r` characters (`:%s/\r//g`). Also, using `sh -x script.sh` can help debug complex scripts.
2. **Crontab Output Control**
A large `/var/spool/clientmqueue` directory was taking up over 100GB. This happened because cron output was being sent as email, but sendmail wasn’t running.
**Solution**: Add `> /dev/null 2>&1` to the crontab command to suppress output, or manually delete the files if needed.
3. **Slow Telnet/SSH Connections**
A colleague experienced slow telnet connections to a server. After checking, I found that DNS resolution was failing.
**Solution**: Modify `/etc/hosts` to map IP addresses to hostnames, or comment out the `nameserver` in `/etc/resolv.conf`.
4. **Read-Only Filesystem**
MySQL failed to create a table due to a "Read-only filesystem" error. After checking permissions, it turned out the filesystem was mounted as read-only.
**Solution**: Restart the machine or remount the filesystem using `mount -o remount,rw /mountpoint`.
5. **Deleted File Not Releasing Disk Space**
A deleted file still occupied disk space because it was being actively used by a process.
**Solution**: Use `lsof | grep deleted` to find the process holding the file, then kill it or redirect `/proc/pid/fd/x` to release the space.
6. **Slow `find` Command Performance**
A nightly cleanup script using `find` caused high load.
**Solution**: Replace `find` with `ls` and `grep` for better performance, especially when dealing with many small files.
7. **Unable to Get Gateway MAC Address**
The gateway MAC address wasn’t being resolved, causing network issues.
**Solution**: Manually bind the MAC address using `arp -s`.
8. **HTTP Service Fails to Start**
Apache couldn’t start due to port conflicts.
**Solution**: Check `netstat` for port usage and disable duplicate `Listen` directives in configuration files.
9. **Too Many Open Files**
An application hit the "Too many open files" limit.
**Solution**: Update `/etc/security/limits.conf` and set `ulimit` in user profiles to increase the maximum number of open files.
10. **Disk Space Issues from ibdata1 and mysql-bin Logs**
Large `ibdata1` and `mysql-bin` files caused disk space alarms.
**Solution**: For `ibdata1`, export and rebuild the database. For `mysql-bin`, adjust `expire_logs_days` in `my.cnf` or manually purge old logs.
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### Troubleshooting Summary Table
| Serial Number | Failure Point | Analysis & Resolution |
|---------------|----------------|------------------------|
| 1 | Hard drive not detected during installation | Enter BIOS settings and set hard drive to compatibility mode |
| 2 | Installation halted after partitioning | Ensure root and swap partitions are created |
| 3 | Confusion during software selection | Gain more experience through repeated installations |
| 4 | Proxy filtering rules not working | Check module loading, default policies, syntax, and rule order |
| 5 | DMZ service inaccessible | Disable iptables temporarily to test connectivity |
| 6 | Rules lost after restart | Enable `IPTABLES_SAVE_ON_RESTART=yes` and save rules |
| 7 | VLAN cannot access external network | Set correct gateway for the VLAN |
| 8 | Named service fails to start | Check for missing files and correct permissions |
| 9 | DNS resolution failure | Verify zone files, configuration, and resolv.conf |
| 10 | DHCP no subnet declaration | Ensure eth0 IP is within the defined scope |
| 11 | Only one scope assigned | Use super-scope with multiple NICs |
| 12 | MySQL installation dependencies | Install required libraries and follow dependency order |
| 13 | Web page not displayed | Correct `DocumentRoot` path in `httpd.conf` |
| 14 | Samba shared directory not accessible | Temporarily disable iptables |
| 15 | NT_STATUS_BAD_NETWORK_NAME | Confirm shared directory exists |
| 16 | NT_STATUS_ACCESS_DENIED | Check user credentials or firewall |
| 17 | NT_STATUS_LOGON_FAILURE | Ensure user has access rights |
| 18 | FTP upload rejected | Grant write permissions to the upload directory |
| 19 | Root user denied access | Disable SELinux if enabled |
| 20 | Mail not received | Verify pop3 service is running |
| 21 | NFS mount hangs | Start `portmap` service |
| 22 | NFS mount works locally but not on other clients | Disable iptables on client machines |
By learning from these real-world scenarios, we can build a stronger foundation in Linux administration. Remember, every problem is an opportunity to grow and refine your skills. Keep experimenting, stay curious, and never stop learning.