Alternate method of running swapon?

[Jeffrey Walton]

On Wed, Jan 8, 2020 at 1:23 PM Valentin Vidić
<vvidic at valentin-vidic.from.hr> wrote:
>
> On Wed, Jan 08, 2020 at 01:09:23PM -0500, Jeffrey Walton wrote:
> > Hi Everyone,
> >
> > I work with an open source project. We have a VM but it is low-end.
> > The machine suffers OOM kills. We don't have access to /etc/fstab.
> > Everything is an upsell with the VPS provider.
> >
> > I'm trying to setup a swapfile during startup using Systemd but:
> >
> >     # swapon /swapfile
> >     swapon: /swapfile: swapon failed: Operation not permitted
> >
> > This may be useful:
> >
> > # command -v swapon
> > /sbin/swapon
> > # file /sbin/swapo
> > swapoff  swapon
> > # file /sbin/swapon
> > /sbin/swapon: ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
> > dynamically linked (uses shared libs), for GNU/Linux 2.6.32,
> > BuildID[sha1]=a4891bc4dcfc533c61d76aa3e69870ab35d90c89, stripped
> >
> > My question is, is there a way to sidestep the restriction? Is it
> > possible to ask the kernel to use the swapfile without using the
> > command?
>
> You can try running for more details:
>
>  # strace swapon /swapfile
>
> but the swap functionality is probably disabled in the kernel itself.

Thanks Valentin.

Here is the full Pastebin: https://pastebin.com/hHAv5T0N .

I believe this is the relevant part from the Pastebin:

readlink("/swapfile", 0x7ffefb4c0810, 4096) = -1 EINVAL (Invalid argument)
stat("/swapfile", {st_mode=S_IFREG|0600, st_size=2147483648, ...}) = 0
open("/swapfile", O_RDONLY)             = 3
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
65536) = 65536
close(3)                                = 0
swapon("/swapfile", 0)                  = -1 EPERM (Operation not permitted)
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=2502, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x7fdbd8207000
read(3, "# Locale name alias data base.\n#"..., 4096) = 2502
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7fdbd8207000, 4096)            = 0
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/util-linux.mo",
O_RDONLY) = -1 ENOENT (No such file or directory)
...

Jeff