gcc -lGL -lX11 glinfo.c -o glinfo && ./glinfo

glinfo.c

#include <GL/gl.h>
#include <GL/glx.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
  Display *dpy = XOpenDisplay(NULL);
  if(!dpy) {
    puts("cannot XOpenDisplay");
    return 1;
  }

  int scrnum = DefaultScreen(dpy);
  Window root = RootWindow(dpy, scrnum);

  int attrib[] = {
    GLX_RGBA,
    GLX_RED_SIZE, 1,
    GLX_GREEN_SIZE, 1,
    GLX_BLUE_SIZE, 1,
    GLX_DOUBLEBUFFER,
    None
  };
  XVisualInfo *visinfo = glXChooseVisual(dpy, scrnum, attrib);
  if(!visinfo) {
     puts("cannot get an RGB, double-buffered visual");
     return 1;
  }

  XSetWindowAttributes attr;
  attr.background_pixel = 0;
  attr.border_pixel = 0;
  attr.colormap = XCreateColormap(dpy, root, visinfo->visual, AllocNone);
  attr.event_mask = StructureNotifyMask | ExposureMask;
  unsigned long mask = CWBackPixel | CWBorderPixel | CWColormap | CWEventMask;
  Window win = XCreateWindow(dpy, root, 0, 0, 100, 100,
                             0, visinfo->depth, InputOutput,
                             visinfo->visual, mask, &attr);

  GLXContext ctx = glXCreateContext(dpy, visinfo, NULL, True);
  if(!ctx) {
    puts("cannot glXCreateContext");
    return 1;
  }

  glXMakeCurrent(dpy, win, ctx);

  int max_texture_size;
  glGetIntegerv(GL_MAX_TEXTURE_SIZE, &max_texture_size);
  printf("glGetIntegerv(GL_MAX_TEXTURE_SIZE) = %d\n", max_texture_size);

  return 0;
}