tail functionality in Go

nxadm/tail provides a Go library that emulates the features of the BSD tail program. The library comes with full support for truncation/move detection as it is designed to work with log rotation tools. The library works on all operating systems supported by Go, including POSIX systems like Linux, *BSD, MacOS, and MS Windows. Go 1.12 is the oldest compiler release supported.

A simple example:

// Create a tail
t, err := tail.TailFile(
	"/var/log/nginx.log", tail.Config{Follow: true, ReOpen: true})
if err != nil {
    panic(err)
}

// Print the text of each received line
for line := range t.Lines {
    fmt.Println(line.Text)
}

See API documentation.

Installing

go get github.com/nxadm/tail/...

History

This project is an active, drop-in replacement for the abandoned Go tail library at hpcloud. Next to addressing open issues/PRs of the original project, nxadm/tail continues the development by keeping up to date with the Go toolchain (e.g. go modules) and dependencies, completing the documentation, adding features and fixing bugs.

Examples

Examples, e.g. used to debug an issue, are kept in the examples directory.

Page Cache Control

When tailing many files in memory-constrained environments (e.g. Kubernetes pods), the OS page cache can grow unbounded and cause OOM kills. The DropPageCache option advises the kernel to release cached pages after reading, keeping memory usage stable.

t, err := tail.TailFile("/var/log/app.log", tail.Config{
    Follow:        true,
    ReOpen:        true,
    DropPageCache: true,
})

When enabled, the following optimizations are applied:

Platform	Mechanism	Effect
Linux	fadvise(FADV_SEQUENTIAL)	Hints sequential access for better readahead and eviction
Linux	fcntl(O_NOATIME)	Suppresses access-time updates to reduce inode writeback
Linux, FreeBSD, NetBSD	fadvise(FADV_DONTNEED)	Evicts read pages from the page cache (every 64KB, at EOF, and on close)
macOS	fcntl(F_NOCACHE)	Bypasses the unified buffer cache entirely