Debian swapper如何监控与管理 - 问答

Monitoring Debian Swapper (Swap Space)
Monitoring swap space is essential to understand system memory pressure and performance. The following tools and commands help track swap usage in Debian:

free Command: Provides a summary of memory and swap usage in a human-readable format. The -h flag displays values in GB/MB for better readability.
```
free -h
```
Output includes total swap size, used swap, and free swap (e.g., Swap: 2.0G 1.0G 1.0G).
swapon --show Command: Lists all currently enabled swap partitions/files with details like device name, type, size, used space, and priority.
```
swapon --show
```
Example output:
```
NAME      TYPE      SIZE USED PRIO
/dev/sda2 partition 2G   0B   -2
/swapfile file      1G   512M 10
```
vmstat Command: Displays real-time virtual memory statistics, including swap usage (si = swap in, so = swap out). The 1 flag updates stats every second.
```
vmstat 1
```
Focus on the si and so columns to monitor active swap activity.
top/htop Commands: Real-time system monitors that include swap usage in their output. htop (install via sudo apt install htop) provides a more intuitive interface with color-coded metrics.
/proc/meminfo File: A detailed pseudo-file with swap-specific entries (e.g., SwapTotal, SwapFree). View it with:
```
cat /proc/meminfo | grep Swap
```
Graphical Tools: Tools like gnome-system-monitor (GUI) or conky (lightweight desktop widget) offer visualizations of swap usage for easier interpretation.

Managing Debian Swapper (Swap Space)
Managing swap involves creating, enabling/disabling, and configuring swap space to optimize system performance:

Creating Swap Space: You can create a swap partition (using fdisk/gparted) or a swap file (more flexible). For swap files:
1. Create a file (e.g., 1GB):
```
sudo fallocate -l 1G /swapfile  # or `sudo dd if=/dev/zero of=/swapfile bs=1M count=1024`
```
2. Set strict permissions (only root can access):
```
sudo chmod 600 /swapfile
```
3. Format the file as swap:
```
sudo mkswap /swapfile
```
4. Enable the swap file:
```
sudo swapon /swapfile
```

Enabling/Disabling Swap:

Temporarily enable a swap file/partition:

sudo swapon /swapfile  # or /dev/sdXY for partitions

Temporarily disable:
```
sudo swapoff /swapfile  # or /dev/sdXY
```
Disable all swap temporarily:
```
sudo swapoff -a
```

Persistent Configuration: To retain swap settings after reboot, add an entry to /etc/fstab. For a swap file:
```
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
```
For a partition, use its UUID (find with sudo blkid) or device name:
```
UUID=1234-5678-90AB none swap sw 0 0
```
Adjusting Swappiness:
Swappiness (vm.swappiness) controls how aggressively the kernel uses swap (range: 0–100). A lower value prioritizes physical memory; a higher value increases swap usage.
- View current value:
```
cat /proc/sys/vm/swappiness
```
- Temporarily change (e.g., to 10):
```
sudo sysctl vm.swappiness=10
```
- Permanently change: Edit /etc/sysctl.conf and add:
```
vm.swappiness=10
```
  Apply changes with:
```
sudo sysctl -p
```
Deleting Swap Space:
- For swap files: Disable and remove the file.
```
sudo swapoff /swapfile
sudo rm /swapfile
```
  Remove the /etc/fstab entry.
- For partitions: Disable the partition, delete its /etc/fstab entry, and optionally repurpose the disk space.[1,3,4,6,7,9,10,11,12]

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