Sysfs is a virtual filesystem in Linux that provides a structured interface for accessing kernel data and information about devices, drivers, and other kernel entities. In this article, we'll delve into the intricacies of sysfs, its structure, common conventions, and practical examples to demonstrate its usage.
1. Overview of Sysfs:
- Sysfs, short for system filesystem, is mounted at `/sys` and presents a hierarchical view of kernel objects as directories and files.
- It provides a unified interface for userspace programs to interact with kernel data, including device attributes, driver parameters, and system information.
2. Structure of Sysfs:
- Sysfs organizes kernel objects into a tree-like structure, with each node representing a specific entity.
- Directories in sysfs correspond to kernel objects, while files within those directories expose attributes and control interfaces.
3. Common Sysfs Entities:
- Devices: Information about hardware devices, such as PCI cards, USB devices, and network interfaces.
- Drivers: Details about kernel drivers and their associated devices.
- Bus: Information about system buses, including PCI, USB, and ACPI.
- Power Management: Controls for system power states and device power management.
4. Example: Reading Device Information from Sysfs
- Let's demonstrate how to retrieve information about a network interface (e.g., `eth0`) using sysfs in a Bash script:
#!/bin/bash
interface="eth0"
sysfs_path="/sys/class/net/$interface"
if [ -d "$sysfs_path" ]; then
echo "Network Interface: $interface"
cat "$sysfs_path/address" # MAC address
cat "$sysfs_path/type" # Interface type
cat "$sysfs_path/operstate" # Operational state
else
echo "Network interface not found: $interface"
fi
5. Example: Setting Driver Parameters via Sysfs
- Let's demonstrate how to set a driver parameter (e.g., maximum readahead) using sysfs in a Bash script:
#!/bin/bash
driver="sd"
parameter="max_sectors_kb"
value="1024"
sysfs_path="/sys/class/block/$driver/$driver$1"
if [ -d "$sysfs_path" ]; then
echo "Setting $parameter to $value for $driver$1"
echo "$value" > "$sysfs_path/$parameter"
else
echo "Driver $driver$1 not found"
fi
- Sysfs provides a powerful interface for accessing kernel data and managing system resources in Linux.
- By leveraging sysfs, developers can retrieve information about devices, drivers, and system configuration, as well as modify driver parameters and control system behavior.
- With practical examples, we've demonstrated how to interact with sysfs using Bash scripts, showcasing its versatility and utility in system administration and development tasks.
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