moving a file in a container to a folder that has a mounted volume docker

Question

am trying to run a golang application on docker. But when i try to move created file in the container to the folder the created volume is mounted on,i get an error :rename /mygo/newt /mygo/store/newt: invalid cross-device link

my golang code

package main

import (
    "bufio"
    "fmt"
    "os"
    "path/filepath"
    "strings"
)

func main() {

    for {

        fmt.Println("do you want to create a file,y for yes, n for no")
        var ans string
        fmt.Scanln(&ans)
        if ans == "y" {
            var userFile string
            fmt.Println("enter name of file")
            fmt.Scanln(&userFile)
            myfile, err := os.Create(userFile)
            if err != nil {
                fmt.Printf("error creating file::%v\n", err)
                return
            }
            fmt.Println("enter text to write in file")
            reader := bufio.NewReader(os.Stdin)
            input, err := reader.ReadString('\t')
            if err != nil {
                fmt.Println("an error occured while reading::", err)
                return
            }
            input = strings.TrimSuffix(input, "\t")
            num, err := myfile.WriteString(input)
            if err != nil {
                fmt.Println("error while writing to file", err)
            }
            fmt.Printf("%v characters entered \n", num)
            defer myfile.Close()
            fmt.Println("created a file", userFile)
            fmt.Println("===========")
            fmt.Println("moving file to default folder")
            pwd, err_pwd := os.Getwd()
            if err_pwd != nil {
                fmt.Printf("could not get current working directory::%v\n", err_pwd)
            }

            userFilePath := pwd + "/" + userFile
            fmt.Println(pwd)
            destinationFilePath := pwd + "/store/" + userFile
            //destinationFilePath := pwd + "/default/" + userFile
            err_moving := os.Rename(userFilePath, destinationFilePath)
            if err_moving != nil {
                fmt.Printf("Error occured while moving file::%v\n", err_moving)
                return
            }
            fmt.Println("file moved")
            continue
        }
        pwd, err_pwd := os.Getwd()
        if err_pwd != nil {
            fmt.Printf("could not get current working directory::%v\n", err_pwd)
        }
        fmt.Println("enter full path to move to default location")
        var userFilePath string
        fmt.Scanln(&userFilePath)
        userFileName := filepath.Base(userFilePath)
        destinationFilePath := pwd + "/" + userFileName
        err_move := os.Rename(userFilePath, destinationFilePath)
        if err_move != nil {
            fmt.Printf("error occured while moving file:::%v", err_move)
            return
        }
        fmt.Println("file moved")
        continue
    }
}

dockerfile

FROM golang 

WORKDIR /mygo

COPY . .
RUN go build -o app
CMD ["./app"]

running the container

the program exits after the error

score 0 · Accepted Answer · answered Oct 07 '22 at 02:03

There are two ways to "rename" a file in Linux.

Move the directory entry to a new place, but keep the file contents unchanged.

This has the advantage of being fast. It has the disadvantage that it doesn't work when moving a file from one filesystem to another.
Create a new file, copy the data to the new file, and delete the old file.

However, it will work if the source and destination are on two different filesystems.

Method #1 will not work in this case. You need method #2.

More resources:

This golang-dev discussion explains why this happens.
This question talks about the same problem, but in the context of C++.
Go uses the renameat() syscall internally. This manual page explains how it works. The specific error you're encountering is the EXDEV error: "oldpath and newpath are not on the same mounted filesystem. (Linux permits a filesystem to be mounted at multiple points, but rename() does not work across different mount points, even if the same filesystem is mounted on both.)"

so there has been no implementation for this issue yet,right?, copying and deleting the previous file worked — Bethel-m, Oct 07 '22 at 09:42
@Bethel-m Yeah, that's the best way to do it as far as I know. — Nick ODell, Oct 07 '22 at 16:56

moving a file in a container to a folder that has a mounted volume docker

1 Answers1